Preheat the oven: Set oven to 375°F (190°C).
Prepare the vegetables: Heat olive oil in an oven-safe skillet over medium heat. Sauté zucchini (and onion, if using) until slightly softened, about 3–4 minutes. Add cherry tomatoes and cook for another 2 minutes.
Mix the eggs: In a bowl, whisk together eggs, milk or cream, salt, and pepper.
Combine and cook: Pour the egg mixture over the sautéed vegetables in the skillet. Sprinkle feta cheese on top. Allow to cook on the stovetop for 2–3 minutes until the edges start to set.
Bake: Transfer the skillet to the preheated oven. Bake for 12–15 minutes, or until the frittata is fully set and lightly golden on top.
Serve: Remove from oven, let cool slightly, slice, and garnish with fresh herbs if desired.
Serving and Storage Tips
