Preheat the oven's broiler and set the oven rack about 6 inches from the heat source.
Place bun halves, crust sides down, onto a baking sheet. Broil the buns until just toasted, about 1 minute. Watch them carefully, they burn easily. Set the toasted buns aside.
Turn oven heat to 350 degrees F (175 degrees C).
In a large skillet over medium heat, cook and stir the ground beef until the meat is browned and crumbly, about 10 minutes. Drain excess grease, and stir in the onion. Cook and stir the beef mixture until the onion is translucent, about 5 more minutes, then stir in the pizza sauce, Parmesan cheese, Italian seasoning, garlic powder, onion powder, crushed red pepper flakes, and paprika. Bring the sauce to a boil, and simmer for 10 to 15 minutes to blend the flavors, stirring often.
Spoon the beef sauce over the buns on the baking sheet, and top each bun with about 1/4 cup of the shredded mozzarella cheese. Return the buns to the oven, and bake until the cheese is bubbly and lightly browned, about 10 minutes.