Heat an ovenproof skillet (I like to use my 12” cast iron frying pan) over medium-high heat and turn the broiler on high to preheat the oven.
Add sausage to pan and break apart with a wooden spoon or spatula while it cooks (no oil is necessary here if you have a nice fatty sausage; if you are using a very lean sausage, add a tablespoon of coconut oil).
Add onion, pepper, and mushroom and sauté, stirring occasionally, until vegetables are cooked (8-10 minutes).
Add beaten eggs. Let cook on stovetop 1-2 minutes, stirring a couple of times.
Place skillet in oven and broil until eggs are completely cooked, puffed up and starting to brown on top (about 7-10 minutes, varies oven to oven so watch carefully).
Notes
Serve immediately or store in the refrigerator for up to 5 days.