Preheat an electric skillet to 300 F. Add the olive oil, the red onions, mushrooms, red pepper and sausage to the skillet. Lightly salt the mixture and cook, stirring occasionally and using the back of a spoon or a spatula to break up the chunks of sausage, 3 to 5 minutes or until the onions have softened, the mushrooms are lightly browned and the sausage is no longer pink.
Add the eggs and stir immediately to incorporate them into the mixture. Add the cheese and spinach and fold everything together.
As soon as the eggs have set, the cheese has started to melt and the spinach has wilted, the dish is ready to serve. Season to taste with salt and pepper.
Serves 6 to 8.
Adapted from The Foundry Grill at the Sundance Resort in Sundance, Utah.