This is a festive-looking appetizer with the green and red vegetables used. They work well as a finger food, too.
Spray 12 muffin cups with canola cooking spray (or line with foil cupcake papers). Preheat oven to 400°F.
Add a zucchini slice to the bottom of each prepared muffin cup. Top zucchini slices with the bell pepper and green onion (distribute evenly between the 12 muffin cups).
In mixing bowl, beat eggs, egg substitute, salt, pepper, and oregano on medium-low speed until completely blended (a couple of minutes). Spoon about 1 1/2 tablespoons of the egg mixture into each of the muffin cups. Sprinkle the cheese evenly over the top of the cups.
Bake until frittatas are set, about 10-12 minutes. Serve warm and use a small rubber scraper to remove the frittatas from the pan (unless you used foil cupcake liners).