Steam the cauliflower by placing the cut florets in a microwave-safe bowl with 1 cup of water. Cover with a damp paper towel and microwave on high for about 3 minutes, or until the cauliflower is tender. Be careful not to overcook!

Drain the cauliflower and pat it dry with a paper towel. Set it aside.

Preheat the oven to 400°F.

In a large skillet over medium-high heat, cook the Italian sausage for about 15 minutes. Once it’s cooked, drain any excess fat and set aside.

In the same skillet, add the olive oil and sauté the mushrooms over medium-high heat for 10 minutes to remove the excess water. Once done, set them aside.

Prepare a 13x9-inch casserole dish by spraying it with non-stick spray, then spread ½ cup of pasta sauce on the bottom.

In a large bowl, combine the cauliflower, cooked Italian sausage, sautéed mushrooms, and green peppers. Toss everything together until well mixed.

Spread half of the mixture into the casserole dish. Top with ½ cup of pasta sauce, followed by half of the pepperoni (press them down into the mixture), and 6 ounces of shredded mozzarella cheese.

Next, spread the remaining mixture over the cheese, followed by the remaining pepperoni (save 10 slices for the top), the remaining ½ cup of pasta sauce, and 6 ounces of mozzarella cheese.

In a small bowl, mix the Parmesan cheese and Italian seasoning together.

Sprinkle the Parmesan mixture over the casserole and top with the 10 slices of pepperoni.

Place the casserole in the oven and bake for 30 minutes, or until it’s heated through and the cheese is fully melted.