Preheat the oven to 400°F.
Prepare the patties: In a large bowl, mix the ground beef, finely diced onions, and salt. Roll into 1.5-ounce balls, press slightly to form mini patties, and place them on a lined baking sheet.
Bake the patties at 400°F for 15 minutes or until fully cooked.
Make the sauce by mixing all sauce ingredients in a bowl until well combined. Set aside.
Assemble the bites: Once patties are cooked, remove them from the oven and pat off excess grease. Cut cheese slices into four small squares and place one on each patty. Return to the warm oven (with the heat off) to let the cheese melt.
Stack and serve: Top each burger with chopped lettuce and a dill pickle slice. Secure with a skewer and serve with the signature sauce.