1. Preheat oven to 400 degrees.
2. Warm a skillet, cook Italian sausage completely, drain.
3. Mix sausage, sauce, pepperoni, onions, mushrooms, and peppers together until well combined. Line bottom of pie shell with mixture.
4. Top with the cheese, then seal with the flat pie shell top. Be sure to poke some ventilation holes.
5. Bake for 50-60 minutes, until the pie crust starts to brown.