Preheat oven to 400°F.
In a mixing bowl, combine the eggs, pepper and salt and whisk together for 30 seconds or until foamy; set aside.
Prepare a 12" oven-safe skillet with non-stick cooking spray and place it over medium heat. Add the sausage and cook for 5 minutes. Remove the sausage from the pan and place it onto paper towel-lined plate and set aside.
Blot the excess oil from the skillet with a paper towel; add the onions and mushrooms and cook for 1 to 2 minutes. Add the sausage, cheese and eggs to skillet; do not stir the eggs once they are in the pan.
Place the skillet into the oven and bake for 20 to 25 minutes.
Serve the frittata in the pan while hot from the oven, along with fresh fruit, English muffins or whole wheat toast.