In a skillet over medium heat, cook the diced onion until translucent. Add the ground beef, salt, pepper, onion powder, and garlic powder. Cook until the beef is browned. Drain any excess fat.
Brush the tops of the buns with melted butter and sprinkle with sesame seeds. Bake in the preheated oven for 12 minutes or until the buns are golden and the cheese is melted.