Preheat the oven to 375°F (190°C). Cut the tops off the bell peppers and remove the seeds and membranes. Set aside.
In a large skillet over medium heat, cook the ground beef until browned, breaking it up into small pieces as it cooks. Once cooked, drain any excess fat.
Add the diced zucchini, onion powder, garlic powder, dried oregano, paprika, cayenne pepper, salt, and pepper to the skillet. Cook for 3-4 minutes, until the zucchini softens.
In a mixing bowl, combine the cooked quinoa (or brown rice), cooked beef mixture, grated Parmigiano-Reggiano cheese, bread crumbs, basil, sweet paprika, egg, and chopped parsley. Stir well until fully combined.
Spoon the mixture into each bell pepper, packing it tightly to ensure the filling stays in place.
Place the stuffed peppers in a baking dish and cover with foil. Bake for 25 minutes. If desired, remove the foil and sprinkle the shredded cheese on top of each pepper. Return to the oven for another 5 minutes, or until the cheese is melted and bubbly.
Allow the peppers to cool slightly before serving. Garnish with additional parsley if desired.