Combine vinegar, the water, sugar (or honey), garlic, jalapeno, and 3/4 tsp salt in a small saucepan, and bring to a boil. Remove from heat, and let stand 15 minutes. Strain through a fine sieve; discard solids. Let cool completely.
Combine zucchini, radishes, tomatoes, and red onion in a boil. Pour in vinegar mixture, and toss to coat.
Heat olive oil in a grill pan (or heat grill) to medium high. Season chicken with salt and pepper. Working in batches, grill chicken until cooked through, 6 to 7 minutes per side. Transfer to a platter, and let stand 10 minutes. Stir torn mint into relish. Season with salt and pepper, and drizzle with vinegar, if desired. Spoon relish on top of the chicken, and garnish with mint leaves.
Notes
Recipe was adapted from the Clean Slate cookbook from the editors of Martha Stewart Living