Preheat oven to 475°F (246°C).

In a bowl, combine mozzarella cheese, green onions, Parmesan cheese, basil, black pepper, salt, egg whites, and eggs.

Whisk the ingredients together until well combined.

Heat olive oil in a nonstick skillet over medium-high heat.

Add zucchini and green bell pepper to the skillet.

Sauté for 5 minutes, or until vegetables are slightly tender.

Pour the egg mixture into the skillet with the vegetables.

Reduce heat to low and cook for 5 minutes, or until the edges are set.

Remove the skillet from heat.

Wrap the handle of the pan with aluminum foil to protect it from the oven's heat.

Bake at 475°F (246°C) for 8 minutes, or until the center is set.

Remove from oven and let cool slightly.

Cut the frittata into 4 wedges and serve.