Start by bringing a large pot of salted water to a boil. Add the rotini pasta and cook for about 7 minutes until it reaches an al dente texture. Drain thoroughly and set aside.

In a large skillet over medium-high heat, add the ground beef and cook for 5-7 minutes until browned. Drain any excess fat.

Sprinkle in the Italian seasoning, garlic powder, and kosher salt, and stir the mixture. Cook for an additional 2 minutes.

Add the diced onion and green bell pepper. Sauté for about 3-4 minutes until the vegetables are softened.

Pour in the marinara sauce, stirring well. Let it simmer for about 5 minutes.

In a greased 9x13-inch baking dish, mix the cooked pasta with the beef and sauce mixture. Fold in half of the mozzarella cheese.

Sprinkle the remaining mozzarella cheese evenly over the top, followed by a layer of pepperoni slices.

Preheat your oven to 375°F (190°C) and bake for 20-25 minutes until the cheese is bubbling and golden brown.