In a large mixing bowl, combine the lean ground beef, garlic powder, kosher salt, and black pepper. Mix gently until well incorporated.
In a skillet, heat the olive oil over medium heat. Add the diced white onion and sauté for about 5-7 minutes until soft and translucent.
Add the sautéed onions to the beef mixture along with Worcestershire sauce and Dijon mustard. Cook the beef mixture over medium-high heat until browned, about 8-10 minutes.
Preheat your oven to 350°F (175°C). Slice the Hawaiian rolls in half horizontally and place the bottom half in a baking dish. Layer half the cheese, the beef mixture, and the remaining cheese on top.
Combine melted butter, kosher salt, brown sugar, and sesame seeds in a small bowl. Brush this mixture over the top of the sliders.
Cover with aluminum foil and bake for 15 minutes. Remove the foil and bake for an additional 10-15 minutes until golden brown and cheese is melted.
Let the sliders cool briefly, slice into individual sliders, sprinkle with extra sesame seeds if desired, and serve warm.
