Preheat the oven to 350°F (175°C). Lightly grease a baking dish or line it with parchment paper.

In a skillet over medium heat, cook the ground beef and diced onion until the beef is browned and the onion is softened, breaking up the meat as it cooks. Drain any excess grease.

Season the beef with salt, black pepper, and Worcestershire sauce, then stir to combine. Remove from the heat.

Slice the slider buns in half horizontally, keeping the top and bottom halves connected if possible. Place the bottom halves in the prepared baking dish.

Spread the mayonnaise, ketchup, and mustard over the bottom buns, if using. Spoon the beef mixture evenly over the buns.

Top the beef with the halved cheddar slices, then place the top halves of the buns over the cheese.

Brush the tops of the buns with melted butter and sprinkle with sesame seeds.

Bake for 10 to 15 minutes, or until the cheese is melted and the tops are lightly golden.

Remove from the oven, let cool for a few minutes, then slice and serve warm with optional toppings if desired.