Preheat the oven to 375 degrees and lightly grease a loaf pan.
In a large bowl, combine the ground beef, breadcrumbs, egg, Calabrian chili paste, oregano, basil, garlic, onion, salt, and pepper. Mix until evenly combined but do not overwork the meat.
Press half the mixture into the loaf pan. Sprinkle three-quarters of the mozzarella over the surface, then top with the remaining meat mixture and press gently to seal.
Bake for 45 minutes. While the meatloaf bakes, place the red bell peppers directly over a gas burner or under a broiler until the skins char and blister on all sides. Transfer to a bowl, cover for 5 minutes, then peel, seed, and slice the peppers.
Remove the meatloaf from the oven, top with the remaining mozzarella, and return to the oven for 5 more minutes until the cheese melts. Let the meatloaf rest for 10 minutes before slicing. Arrange the charred pepper slices over the top and sprinkle with fresh parsley.