In a large bowl combine the ground beef, seasonings, peanut butter and milk.
Spread the meat mixture on a cookie sheet. Use a rolling pin to roll over the meat and flatten it as much as possible. Bake at 350 degrees for about 10 minutes.
Sprinkle the diced onion all over the top. Bake for about 15 minutes.
Place the cheese slices on the meat and bake for about 5 minutes.
Place the bun tops on the cheese and bake an additional 3-5 minutes.
Slice the meat and place sliders on the bottom buns.