Preheat your oven to 350°F (175°C).

In a large pot, boil water and cook the rotini pasta according to the package instructions until al dente. Drain and set aside.

In a large skillet over medium heat, brown the ground beef. Stir occasionally until fully cooked. Drain any excess fat.

Add the chopped onion and green bell pepper to the skillet with the ground beef. Cook until the veggies are tender.

Stir in the Italian seasoning, garlic powder, kosher salt, and marinara sauce. Let it simmer for a few minutes.

In a large mixing bowl, combine the cooked pasta, pepperoni, and the meat sauce mixture. Stir until everything is well mixed.

Pour half of the mixture into a baking dish. Sprinkle half of the mozzarella cheese on top. Then add the remaining pasta mixture and finally top with the rest of the cheese.

Cover the baking dish with foil and bake for 20 minutes.

Remove the foil and bake for another 10 to 15 minutes until the cheese is bubbly and golden.

Let it cool for a few minutes before serving. Enjoy your cheesy casserole!