Cook beef and drain. Add ground beef, adding salt and pepper to taste. Continue to cook until the meat is cooked through, and the onions are translucent. Drain liquid and grease from ground beef mixture.
Prepare buns. Cut slider buns in half (if not pre-cut). Set the tops of the buns to the side and place bottom half of the buns on a baking dish sheet.
Add cheese. Place 6 American cheese slices on bottom buns and break last slice in half to completely cover buns with cheese.
Add layers. Spread beef and onion mixture over the cheese. Break up the cooked bacon into 12 pieces and place so there will be a slice on each bun. Add pickle, ketchup, and mustard.