Preheat the oven broiler on low.
Don't separate the buns individually. Slice the buns in half creating a top sheet and a bottom sheet.
Mix together the ground beef, steak seasoning, and Worcestershire sauce, season generously salt and pepper. Portion the beef evenly.
Preheat a cast iron skillet or non-stick pan over medium heat. Place the beef portions into the pan and press down using a spatula to flatten them. Cook on both sides for about 20 seconds per side. Then set aside. (Leave the grease in the pan.)
Add the onions to the pan and sauté until golden brown. Add in 1/2 of the butter, take the top sheet of the buns and place into the pan, cook until golden brown then remove and set aside. Do the same with the bottoms of the buns using the remaining butter. Then remove and set aside (make sure all of the onion sticks to the inside of the buns).
Place the burgers onto the bottom sheet of buns and top with cheese. Place underneath the oven broiler to melt. Once melted top with lettuce, pickles, and top bun sheet.
In the meantime, whisk together all of the ingredients for the sauce in a bowl.
Cut the sliders into portions. Spread the sauce on the sliders or on the side.