In a skillet, brown the ground beef and the onions until the beef is fully cooked and the onions are transparent. Drain.
Preheat oven to 325F.
Keeping the 12 dinner rolls together, cut them lengthwise. Place both halves side by side on a large baking sheet. Bottom half should be cut side facing up and top half should be cut side facing down.
Evenly spread the ground beef mixture all over the bottom half of the dinner rolls. Lay cheese slices on top of the ground beef.
Brush the melted butter on the top of the dinner rolls. Sprinkle with sesame seeds
Bake in the oven for 20 minutes. Cheese should be melted and dinner rolls starting to brown.
Evenly place pickles on top of the melted cheese. Sprinkle the chopped lettuce on top.
Flip the top part of the dinner rolls so the cut side is facing up. Evenly spread the Big Mac Sauce or Thousand Island dressing across the cut side of the top half of the dinner rolls.
Place the top half of the dinner rolls on top of the bottom half. Cut into sliders and serve.