Preheat the oven to 350 F.
In a large mixing bowl, add ground beef, salt, pepper, garlic powder and egg. Mix ingredients until fully combined.
Divide the meat in half to form two rectangles. Make the rectangles are a bit bigger than your set of 6 connected dinner rolls, as they will shrink some while cooking.
Place both rectangles on a cookie sheet, and if you like add a pinch full of the chopped onion on top of the meat.
Bake in the preheated oven for 12 minutes. Add 2-3 minutes for well done, or cook to your liking. Add 3 cheese slices to each meat patty and bake another 2-3 minutes, or until cheese has belted
Set out the 2 sets of "6-pack" of the slider buns. Spoon a few Tbsp of Thousand Island dressing on each of the slider bottoms and evenly spread it over all rolls with a spoon.
Once the meat is cooked, place the meat & cheese patties on each of the 2 bottoms of 6-pack bun sets.
Finally, top the burgers with minced onion, pickles and lettuce. Then top it with the top of the slider buns.
Spread the melted butter over the tops of the slider buns and sprinkle the sesame seeds.
Cut the 2 "6-packs" into 12 total sliders and enjoy!