Preheat: Preheat the oven to 200°C.
Preparation: Drizzle some olive oil in a cast-iron pan or baking dish and line it with parchment paper.
Add vegetables: Evenly distribute the spinach, tomato, and yellow bell pepper over the bottom of the pan or baking dish.
Make egg mixture: Beat the eggs with a hand mixer and add the pesto, Parmesan cheese, and half of the crumbled feta. Season with pepper and salt.
Assemble: Pour the egg mixture over the vegetables in the pan or baking dish. Lightly mix everything together and crumble the rest of the feta on top.
Bake: Place the pan or baking dish in the preheated oven and bake the dish for about 20-25 minutes, or until the omelet is set and golden brown.
Serve: Optionally serve with a fresh salad of your choice.
Tips
You can vary with other vegetables such as zucchini or mushrooms. For an extra spicy taste you can add some chili flakes to the egg mixture.