Preheat your oven to 350 F.
Melt some cooking fat in a skillet placed over medium-high heat. Cook the onion, bell peppers, and garlic until soft and fragrant, about 5 minutes.
2 bell peppers, 1 onion, Cooking fat, 2 garlic cloves
Add the mushrooms and spinach and cook for another 2 to 3 minutes. Season everything to taste.
8 to 10 fresh mushrooms, 2 cups baby spinach, Sea salt and freshly ground black pepper
Whisk the eggs together in a big bowl, and add the bell pepper & spinach mixture.
8 eggs
Grease a muffin tin and pour the mixture evenly into the muffin cups.
Place in the oven and bake for 20 to 25 minutes.