Preheat: Preheat the oven to 350 degrees F.
Sauté the onions: Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the diced onion and cook, stirring occasionally, until translucent.
Brown the beef: Add 1½ pounds of ground beef to the skillet. Cook over medium heat, breaking it up with a spatula, until fully browned.
Season: Stir 1 tablespoon garlic powder, 1 teaspoon salt and pepper, and 2 tablespoons Worcestershire sauce until fully combined. Remove from heat.
Slice and toast the rolls: Keep the rolls connected and slice them in half horizontally with a serrated knife to create a top and bottom slab. Place the bottom slab in a 9x13-inch baking dish and bake for 5-10 minutes, just until lightly toasted.
Assemble: Spread half of the cheese over the toasted rolls, then spoon the beef mixture in an even layer over the cheese. Top with the remaining cheese
Melt the cheese: Bake for 10 minutes, or until the cheese is melted.
Add the tops and bake: Place the top slab of rolls over the cheese. Brush with melted butter and sprinkle with sesame seeds. Bake for 5-10 minutes, or until the tops are lightly toasted.
Rest and serve: Let cool for a few minutes, then slice into sliders and serve.
For the burger sauce: Stir all burger sauce ingredients together in a small bowl until smooth. Serve on the side for dipping or spread inside the sliders.