Combine butter, garlic powder, and paprika; set aside. Brown meat; drain fat. Add onion, ketchup, parmesan cheese, garlic powder, fennel seed, and oregano. Simmer for 20 minutes.
Split hamburger buns. Spread about 1 teaspoon of garlic spread on each bun top. Divide meat mixture evenly on bun bottoms. Top meat mixture with a slice of cheese. Top with bun top. Wrap each sandwich in a square of foil.
Bake in 350°F oven for 15 minutes, or until heated through.