Place a large cast iron skillet over medium heat. Add sausage and use a wooden spoon to break into small pieces, until no pink remains. Spread sausage evenly throughout the skillet. Turn heat down to medium-low.
In a large bowl, whisk together eggs, basil, pizza sauce, salt, pepper, and red pepper flakes. Pour mixture into skillet and let cook in the pan for 5 minutes. Then top the frittata with green pepper slices, mushrooms and pepperoni. Place in oven to bake at 20 minutes.
Toss arugula in lemon and olive oil and place on top of frittata before serving!