Start by gathering all your ingredients for the Mushroom Swiss Sliders. Dice the white onion, slice the mushrooms, and measure out your ground beef and seasonings.

In a large skillet over medium heat, combine the lean ground beef, Worcestershire sauce, garlic powder, salt, and ground pepper. Cook for 7-10 minutes until browned and no longer pink, then transfer to a bowl to keep warm.

Using the same skillet, melt 2 tablespoons of butter over medium heat. Add the diced white onion and sliced mushrooms, sauté for 5-7 minutes until tender.

Preheat your oven to 350°F (175°C). Slice the King's Hawaiian rolls in half and arrange the bottom halves in a baking dish. Layer the cooked beef mixture, followed by the sautéed mushrooms and onions, and top generously with Swiss cheese slices.

Cover with aluminum foil and bake for 30 minutes, then remove the foil and bake uncovered for an additional 5-10 minutes until the cheese is melted and bubbly.

Let the sliders cool for a few minutes, then sprinkle sesame seeds on top if desired. Serve warm.