Preheat oven to 350 degrees F (175 degrees C). Prepare 12 muffin cups with cooking spray.
Whisk egg whites, eggs, and half-and-half together in a bowl. Stir zucchini, green onion, and cheese into the egg mixture; pour into prepared muffin cups.
Bake in preheated oven until set in the middle, 30 to 35 minutes.