Heat a large skillet over medium high heat. Spray with cooking spray and add onion. Saute 5 minutes, or until onion has softened.
In a large bowl, mix until just combined the ground beef, sauteed onion, breadcrumbs, eggs, ketchup, pickle relish, and mustard.
Spray slider pan or skillet with cooking spray.
Scoop ¼ sized portions and place sliders in slider frying pan or shape into small burgers and place in hot skillet. Cook for 5-7 minutes, or until desired doneness.
Toast slider buns and assemble burger topping with cheese and bacon.
Notes
If using a slider pan, there is no need to flip the sliders to cook each side. The slider pan has a press that goes on top of the burger and allows the slider to cook through evenly.
If using a skillet, cook for 4 minutes on each side, or until desired doneness.