Preheat your oven to 350°F (175°C).

In a large bowl, mix ground beef with salt and pepper. Form into small patties (about two ounces each).

Heat a skillet over medium heat and cook patties for about 4 minutes on each side until desired doneness. Add cheese during the last minute to melt.

Slice buns in half and assemble by placing a patty on the bottom half, adding ketchup, mustard, and pickled onions if using. Cap with bun tops.

Place assembled sliders in a baking dish and bake for 5 minutes until warmed through.