How to Make It
Preheat oven to 350°F. Heat 2 tablespoons oil in a 10-inch ovenproof skillet over medium. Add zucchini, onion, oregano, and garlic and cook, stirring often, until vegetables are slightly softened, 8 to 10 minutes.
Whisk eggs, salt, and crushed red pepper until combined. Add remaining 2 tablespoons oil to skillet, tilting to distribute. Pour egg mixture over vegetables and shake skillet to help eggs settle. Cook over medium until edges begin to set, 2 to 3 minutes. Top with cheese.
Transfer skillet to oven and cook until top is just set, 13 to 15 minutes. Let cool slightly.
Gently slide frittata out of skillet and season with more crushed red pepper. Serve with salad.