Heat a large skillet on medium heat and add in the chopped onions and lean ground beef. Break up the ground beef and add the salt, onion powder, and garlic powder. Stir to combine and cook the ground beef until it is 75% done.
If your ground beef is fatty or put off a lot of juices (more than a ¼ cup or so), drain the meat. I did not have to do this with the 90/10 ground beef.
Add in the pickle juice, ketchup, mayonnaise, apple cider vinegar, mustard, sweet pickle relish, and chopped dill pickles. Stir to combine and simmer for 7-10 minutes uncovered. The sauce will start out fairly thin, but thickens as it simmers.
Add 4 slices of American cheese on top of the sloppy joe mixture and cover with a lid. Turn the heat off and let the cheese slightly melt.
Toast the buns under the broiler for 2-5 minutes. You want them to be lightly toasted so they don't disintegrate when you put the sloppy joe mixture on. Add some shredded lettuce to the bottom of the bun.
Once the cheese has slightly melted, scoop out about ¾ cup of the Big Mac sloppy joe mixture and put it on the bun. Try to get some cheese with every scoop. Top with pickle slices and some more lettuce and then the top of the bun.