Prepare the garlic herb butter by combining softened unsalted butter, minced garlic, and chopped fresh parsley in a bowl. Mix well and set aside.

Toast the hamburger buns with garlic herb butter in a skillet over medium heat until golden brown.

Mix lean ground beef, chopped onion, garlic powder, Italian seasoning, salt, and pepper in a bowl and shape into four patties.

Cook the patties in a skillet over medium-high heat with olive oil, about 4-5 minutes on each side until cooked through.

Add pizza sauce, fresh basil, mozzarella cheese, and pepperoni to the patties in the last minute of cooking to melt the cheese.

Assemble by placing cooked patties on toasted buns, topping with the other half of the bun, and serve hot.