Spray a 7-inch round baking dish with zero-calorie nonstick cooking spray.
In a large bowl, whisk egg whites until frothy. Add in spinach, tomatoes, onion, salt, and pepper. Stir until combined.
Pour the egg mixture into the prepared dish.
Place in the air fryer basket and cook for 20 minutes until the center is set.
Notes
For Flex™ Patients: 6 servings of protein and 1 serving of vegetables. Recipe Yields: 1/3 of frittata equals 2 servings of protein and 1/2 serving of vegetables.