Steps
1. Preheat your oven to 375°F (190°C).
2. In a small oven-safe skillet, heat the olive oil over medium heat.
3. Add the diced onion and bell pepper, sautéing until softened (about 3-4 minutes).
4. Stir in the chopped spinach and cook until wilted.
5. In a bowl, whisk the eggs, then add salt and pepper. Pour the egg mixture over the sautéed vegetables in the skillet.
6. Cook on the stovetop for 2-3 minutes until the edges start to set.
7. Sprinkle cheese on top, then transfer the skillet to the oven.
8. Bake for 10-12 minutes until the frittata is fully set and golden on top.
9. Let it cool slightly before slicing and serving.