In a large skillet over medium heat, cook the ground beef (or turkey) until browned. Drain any excess fat.
Add the diced onion and red bell pepper to the skillet. Sauté until the vegetables are soft, about 5 minutes.
Stir in the pizza sauce, Italian seasoning, salt, and pepper. Allow the mixture to simmer for another 5 minutes.
In a large casserole dish, spread half of the sauce mixture evenly on the bottom.
Layer half of the tater tots over the sauce, followed by a layer of half of the mozzarella cheese, and half of the pepperoni slices.
Repeat the layers with the remaining sauce, tater tots, mozzarella, and pepperoni, finishing with a generous sprinkle of grated Parmesan cheese on top.
Bake in the preheated oven for 25-30 minutes, or until the tater tots are golden brown and the cheese is bubbly.
Remove from the oven and let it cool for a few minutes before slicing.