Preheat the oven to 350 degrees.
In a bowl combine the beef, salt, pepper and bbq rub.
Press the meat onto a parchment lined being pan making sure to press it out to the same size as the slider buns package.
Brush the beef with 1/4 cup ketchup and bake in the oven for 12-15 minutes then drain juices from the baking sheet pan.
As the beef is cooking, warm the olive oil until hot and then add the diced onion and brown sugar, cooking and stirring until golden brown, about 12 minutes.
Slice the buns long ways and set the lid part to the side, keeping the base part on the white cardboard and then to a baking sheet pan. The cardboard will help to lift the hot sliders.
In a small bowl combine the mayo, ketchup and relish. Spread evenly over the bottom part of the slider buns.
Liberally add some of the grilled onions on top of the sauce.
Lay the meat on top of the sauce and onions and then top with the cheese.
Place the top part of the bun on top of the cheese and brush with the melted butter mixture.
Sprinkle with sesame seeds and bake for about 15 minutes.
Carefully slice and serve at once.