1. Coat a 10-inch non-stick skillet with non-stick cooking spray. Over medium heat sauté onion and zucchini until softened and slightly browned, about 4-5 minutes, stirring frequently.
2. In a mixing bowl, whisk eggs, salt and pepper.
3. Pour eggs over zucchini. Top with cheese. Cover the pan and cook over medium-low heat until the edges of the frittata begin to brown and the center has set and has slightly puffed, about 8 minutes.
4. To cut frittata, turn out onto cutting board, top side up. Cut into wedges and serve! If desired, top with ripe tomato and torn basil.