Preheat oven to 350°F (175°C). In a large skillet over medium-high heat, brown the ground beef with the diced onion until the beef is no longer pink and the onion is soft. Drain excess grease. Stir in 1 tbsp Worcestershire sauce, garlic powder, salt, and pepper.

Without separating the rolls, slice the entire slab of Hawaiian rolls in half horizontally. Place the bottom section in a 9x13 inch baking dish. Spread the beef mixture evenly over the rolls. Top with a layer of pickle slices, then a layer of cheddar cheese. Place the top half of the rolls over the cheese.

In a small bowl, whisk together the melted butter, 1 tsp Worcestershire sauce, and onion powder. Brush the mixture evenly over the top of the rolls. Sprinkle with sesame seeds.

Cover the baking dish with aluminum foil and bake for 15 minutes. Remove the foil and bake for an additional 5-7 minutes, until the tops are golden brown and the cheese is fully melted. Let rest for a few minutes before serving.