Heat a large skillet over medium heat. Add the chopped onion and cook for three minutes. Add ground beef, salt, pepper, and garlic powder. Cook until the beef is browned and fully cooked.

Carefully remove any extra grease from the skillet. This keeps the sliders from becoming soggy. Stir the beef mixture well and let it cool for a few minutes.

Using a sharp knife, cut the slider buns in half horizontally. Keep the buns connected if possible. Place the bottom half into a lightly greased baking dish.

Spread the cooked beef evenly over the bottom buns. Make sure every slider gets plenty of meat. This creates a thick and satisfying cheeseburger filling.

Lay the cheddar cheese slices over the warm beef. Cover as much of the meat as possible. The cheese will melt beautifully during baking.

Sprinkle chopped pickles over the cheese. Drizzle ketchup and mustard across the top. These simple ingredients add classic cheeseburger flavor.

Place the top half of the slider buns over the filling. Press down gently so everything stays together while baking.

Mix melted butter in a small bowl. Brush it evenly over the tops of the buns. Sprinkle sesame seeds over the buttered surface.

Cover the dish loosely with foil. Bake at 350°F (175°C) for 15 minutes. Remove the foil and bake another five minutes until golden brown.

Remove from the oven and let the sliders rest for two minutes. Slice into individual portions and serve while warm and cheesy.