Preheat Oven: Preheat your oven to 350°F (175°C).
Cook the Beef: In a skillet over medium heat, cook the ground beef with garlic powder, onion powder, salt, and pepper. Break apart the beef as it cooks until it's browned and no longer pink. Drain any excess fat and mix in the diced bell pepper if using.
Prepare the Sliders: Cut the Hawaiian rolls in half without separating them, creating a top and bottom slab. Place the bottom half in a baking dish.
Layer the Ingredients: Spread the cooked beef evenly over the bottom slab of rolls. Place a layer of cheese slices over the beef. Place the top half of the rolls on top.
Make the Butter Topping: Combine melted butter, poppy seeds, dried minced onion, Worcestershire sauce, and garlic powder. Brush this mixture over the tops of the rolls.
Bake: Cover the sliders with foil and bake for 15 minutes. Remove the foil and bake for an additional 5-10 minutes, or until the tops are golden brown and the cheese is melted.
Serve: Let the sliders cool for a few minutes, then cut into individual servings and enjoy while warm and gooey!