Reduce heat to medium high, add 1 Tbsp coconut oil to cast iron skillet and saute onions until translucent. Transfer to the plate with the sausage.
Heat 1 Tbsp coconut oil over medium high heat, add chopped sweet potatoes and cook, stirring occasionally, until tender (about 10 minutes). Sprinkle some rosemary over sweet potatoes. Cover skillet with a lid while cooking.
Add sausage and onions to the cast iron skillet and stir everything.
Crack four eggs over sweet potato hash. Place cast iron skillet in a preheated 425 degrees oven and cook for about 10-15 minutes until eggs are set.