In a 10-in. ovenproof skillet coated with cooking spray, cook onion in oil over medium heat for 2 minutes. Stir in peppers; cook for 3-4 minutes or until crisp-tender. Add garlic; cook 1 minute longer.
In a small bowl, combine the eggs, egg whites, basil, salt and pepper. Stir in mozzarella cheese; pour over pepper mixture. Sprinkle with Parmesan cheese.
Bake, uncovered, at 350° for 20-25 minutes or until a knife inserted near the center comes out clean. Let stand for 5 minutes before cutting. Yield: 6 servings.