Cook zucchini, onion, sweet pepper, and garlic in hot oil in a medium skillet until onion is tender; cool slightly. Combine egg whites, whole egg, milk, and Italian seasoning in a medium mixing bowl; mix well. Stir in cooked vegetables. Pour into four individual (about 4-1/2-inch-diameter) quiche dishes or shallow casseroles.
Bake in a 350 degrees F oven for 15 to 20 minutes or until set. Sprinkle each serving with mozzarella cheese. Let stand 5 minutes before serving. Makes 4 servings.