Parmesan Zucchini and Tomato Gratin

When zucchini and tomatoes are at their peak, this zucchini tomato gratin is exactly what I make. It’s a simple baked zucchini tomato casserole layered with tender zucchini, juicy tomatoes, garlic, and golden Parmesan — light, flavorful, and perfect for weeknight dinners or entertaining.

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If you’ve ever grown zucchini and tomatoes, you know how quickly they take over the kitchen. Every summer, our vegetable garden gives us an abundance of garden-fresh vegetables, especially zucchini, squash, and tomatoes — and this zucchini tomato gratin is one of the first dishes I make on repeat.

I’ve tweaked the layering and seasoning over the years until it became the perfect balance of tender vegetables and a lightly golden, cheesy top. It’s light enough for warm summer evenings, yet cozy enough to serve year-round.

If you have more zucchini than you know what to do with them, have you checked out my Stuffed Zucchini Boats with Yogurt Garlic Sauce and my Stuffed Zucchini Cups?

Key Ingredients (With Helpful Notes)

Here’s what you’ll need. I’m also sharing a few insights from my own kitchen testing to help you get the best results.

• Yellow onion – Adds sweetness and depth. Don’t skip sautéing — it prevents sharp, raw onion flavor.
• Garlic – Fresh garlic makes a huge difference here. Pre-minced works in a pinch, but I prefer freshly minced for aroma.
• Zucchini – Slice thinly and evenly. If they’re too thick, they won’t cook through evenly.
• Tomatoes – I prefer Roma (plum) tomatoes or other firm, meaty varieties like Campari or vine-ripened tomatoes. They hold their shape beautifully while baking and help prevent the zucchini tomato gratin from becoming watery. I recommend avoiding overripe, soft, or mushy tomatoes, as well as large beefsteak varieties with high water content, since they can release too much liquid and make the casserole soggy.
• Parmesan cheese – I always grate my own for better melting and flavor. Pre-shredded can work, but it doesn’t melt as smoothly.
• Oregano – Adds that classic Mediterranean flavor. You can use fresh or dried.
  Optional Add-Ins (if you want to elevate it): I occasionally mix breadcrumbs with the Parmesan before baking for added golden crunch, or finish the gratin with a drizzle of fresh basil pesto for bright Mediterranean flavor.

How to Make Zucchini Tomato Gratin

I’ve tested this recipe enough times to know that keeping it simple is what makes it foolproof. Just four straightforward steps — that’s it.

1. Preheat & Sauté the Aromatics. Preheat your oven. Heat olive oil in a skillet over medium heat. Sauté the onion until soft and translucent, then add the garlic and cook just until fragrant.
   Don’t skip this step — gently softening the onion builds natural sweetness and depth, while the sautéed garlic adds rich, savory flavor to the zucchini tomato gratin.
2. Create the Flavor Base. Spread about one-third of the onion and garlic mixture over the bottom of your baking dish. I’ve found this not only prevents sticking but also ensures every bite of this zucchini tomato gratin has flavor from the bottom up.
3. Layer, Season & Finish. Arrange the zucchini and tomato slices in an alternating, slightly overlapping pattern until the dish is filled. Top with the remaining onion mixture. Drizzle with olive oil, season with salt, pepper, and oregano, and sprinkle evenly with Parmesan. Tip from my kitchen: Layer them snugly — they shrink as they bake.
4. Bake & Rest. Bake until the vegetables are tender and the top is lightly golden. Let the zucchini tomato casserole rest briefly before serving so the juices settle and slicing is easier.

Serving Suggestions

This baked zucchini tomato gratin is incredibly versatile. Here’s how I love serving it:

• Alongside grilled chicken or fish
• As part of a Mediterranean-style spread
• With a simple arugula salad
• Over cooked quinoa or pasta for a light vegetarian main

Sometimes I even serve leftovers with a fried egg on top for brunch — highly recommend.

You can serve this gratin as a side with baked or grilled chicken, meat skewers, fish, etc. It’s a perfect side dish for summer when tomatoes and zucchini are in abundance. It also makes a great side dish to bring to a potluck or a family gathering.

Storing and Reheating

If you happen to have leftovers, here are my suggestions:

• Storing: Let the zucchini tomato gratin cool completely, then refrigerate in an airtight container for up to a few days.
• Reheating: For the best texture, reheat in the oven until warmed through — this helps maintain that lightly golden top. You can microwave it for convenience, but it will be softer.

More Zucchini Recipes:

Zucchini Lasagna Roll-Ups

Stuffed Zucchini Cups

Stuffed Zucchini Boats

Zucchini Soup

If you enjoyed this recipe or any other recipe on my blog, please leave a ⭐ star rating and let me know how it went in the 📝 comments below.

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Parmesan Zucchini and Tomato Gratin

By: Neli Howard

This easy zucchini tomato gratin is layered with fresh zucchini, tomatoes, garlic, and Parmesan for a light, flavorful summer casserole.

Prep Time: 15 minutes minutes

Cook Time: 35 minutes minutes

Total Time: 50 minutes minutes

Servings: 6

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Ingredients  

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• ▢ 2 tablespoons olive oil, divided
• ▢ ½ medium yellow onion, chopped
• ▢ 1 clove garlic, minced
• ▢ 1 medium zucchini, thinly sliced
• ▢ 3 medium tomatoes, thinly sliced
• ▢ Salt and pepper, to taste
• ▢ Oregano, to taste
• ▢ ¼ cup shredded Parmesan cheese

Cook ModePrevent your screen from going dark

Instructions 

• Preheat your oven to 350°F. Heat 1 tablespoon olive oil in a small skillet over medium heat. Add the chopped onion and sauté until soft and translucent, about 3–4 minutes. Stir in the garlic and cook for 30 seconds, until fragrant.
• Spread about one-third of the onion and garlic mixture over the bottom of a medium round tart dish or casserole dish. Layer the zucchini and tomato slices in a circle, alternating 1 slice zucchini and 1 slice tomato, until the dish is filled.
• Spoon the remaining onion and garlic mixture evenly over the top. Drizzle lightly with the remaining olive oil, then season with salt, black pepper, and oregano. Sprinkle the Parmesan evenly over everything.
• Bake for about 35 minutes, or until the vegetables are tender and the top is lightly golden. Let cool for a few minutes before serving.

Video

Notes

• Slice the zucchini and tomatoes evenly so they cook at the same rate.
• If your tomatoes are very juicy, gently pat them dry before layering to prevent excess moisture.

Nutrition

Calories: 80kcal | Carbohydrates: 5g | Protein: 2g | Fat: 6g | Saturated Fat: 1g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 4g | Cholesterol: 4mg | Sodium: 79mg | Potassium: 254mg | Fiber: 1g | Sugar: 3g | Vitamin A: 614IU | Vitamin C: 15mg | Calcium: 51mg | Iron: 0.4mg

Nutrition Disclaimer: Nutritional values are estimates and may vary with ingredients, brands, and portion sizes. For accuracy, use your preferred nutrition calculator.

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Disclaimer: The information provided in this recipe is for informational purposes only and should not be considered medical or nutritional advice. I am not a doctor or a dietitian. Always consult a qualified healthcare provider for personalized guidance regarding your diet or health. For more details, please read my full disclosure page.

Originally published in July 2016. The recipe remains unchanged, but this post has been updated with clearer instructions.