Butterfly slice each chicken breast in half to make four thin pieces. Season with garlic powder, salt and pepper. Brown chicken slices on each side in olive oil, about 2-3 minutes per side. Place in medium baking dish.
Saute zucchini in pan until soft. Add diced tomato, basil, and oregano. Season with salt and pepper. Cook an additional 2-3 minutes. Pour over chicken.
Cook in 325 degrees F oven for 20 minutes. Top with mozzarella cheese. Bake an additional 5 minutes.