1Preheat your oven to 375°F (190°C).
Arrange the halved bell peppers on a baking sheet, cut-side up, and season them with salt and pepper.
In a skillet over medium heat, sauté the diced onions and sliced mushrooms until they are soft and the onions are translucent, about 5 minutes.
Add the chopped spinach to the skillet and cook until just wilted, approximately 1-2 minutes.
Crack the eggs into a bowl and beat them lightly. Season with salt and pepper.
Distribute the sautéed vegetables evenly among the bell pepper halves.
Pour the beaten eggs over the vegetables, filling each pepper half.
Sprinkle the tops of the egg-filled peppers with shredded cheddar cheese.
Bake in the preheated oven for 25-30 minutes, or until the eggs are set and the cheese is melted and slightly golden.
Remove from the oven and let them cool for a few minutes before serving.