In a large skillet heat olive oil over medium high heat.
Add diced onions and cook for 3 minutes.
Add ground beef and salt and continue to cook until meat is cooked through and onions are translucent.
Drain grease from beef.
Preheat oven to 350 degrees F.
Cut slider buns in half setting the tops of the buns to the side.
Place bottom buns on a baking sheet.
Place 6 slices of American cheese on bottom buns and break last slice in half to completely cover buns with cheese.
Spread beef and onion mixture over the cheese.
Using 7 more slices of cheese create a second layer of cheese.
Break up the cooked bacon into 12 pieces and place so there will be a slice on each bun.
Place a pickle slice so there will be one pickle on each bun.
Drizzle with ketchup and mustard.
Place top buns on top of everything.
Cover the sliders with aluminum foil and bake for 15 minutes.
Remove foil and brush buns with melted butter and sprinkle with sesame seeds.
Bake for another 5 minutes or until cheese is completely melted.