In a large skillet 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.
Spread beef and onion mixture over the buns.
Using 7 slices of cheese create a layer of American cheese over the beef.
Place the pickle slices over the cheese.
Drizzle with ketchup, mustard, and secret sauce.
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.