(2 mini frittatas)
Preheat oven to 350°F. Beat eggs, milk, Italian seasoning, salt and pepper in medium bowl until well blended. Add cheeses, squash, spinach and onion; mix well.
Spray 1 (12-cup) muffin tin generously with no stick cooking spray. Spoon about 1/4 cup egg mixture into each cup. Sprinkle with tomatoes.
Bake 20 to 22 minutes or just until eggs are set. Run small knife or spatula around each cup to loosen mini frittatas. Let stand 5 minutes before serving.