Preheat oven to 350 °F (175 C)
In a large frying pan, brown the ground beef along with the onions and garlic.
In a large bowl, mix the ground beef noodles, salt and pepper, half of the mushrooms, half of the pepperoni, 1 cup of grated cheese and tomato sauce.
Pour into the casserole dish and spread out evenly.
Spread the sugar-free pizza sauce over the surface.
Spread the remaining grated cheese evenly over the pizza sauce.
Spread the remaining pepperoni and mushrooms over the cheese.
Bake in the oven for 45 minutes for up to an hour, until the cheese is bubbly and thoroughly melted.
Serve hot.