Tasty mushrooms and peppers make this baked egg dish robust and deliciously good for you.
In an 8-inch cast iron skillet, heat the oil over medium-high heat until hot.
Reduce the heat to medium. Add the onions and sauté for about 2 minutes until onions start to become soft.
Add the peppers and continue cooking until they become soft, about 3 minutes.
Remove the onions and peppers to another dish and set aside.
Place the mushrooms in the skillet to sauté. Only cook a few mushrooms at a time and do not let them touch. Turn them over periodically as they cook. Continue cooking until they are becoming brown on both sides. When done, remove the mushrooms to a separate dish. This step might take 8-10 minutes.
Whisk the eggs in a bowl until frothy.
Add the salt, pepper, and the onions and peppers mixture. Mix to combine.
Pour the egg mixture into the skillet and cook the eggs until nearly set (about 10 minutes).
Add the mushrooms to the top of the frittata.
Broil the frittata on high for 3-5 minutes until completely set. Watch closely as this can burn easily.
Remove from oven and serve.