Preheat oven to 350 degrees and spray a 9x13 inch pan with non stick spray. In a medium sized skillet over medium high heat add the onion and pepper and sauté for 2-3 minutes until almost tender. Add in the mushrooms and garlic and continue to sauté for 2 minutes. Add spinach and sausage and cook until heated through.
Spread evenly on the bottom of the 9x13 inch pan. Pour the eggs on top of the sausage mixture. Bake for 25-30 minutes or until eggs are cooked throughout.