Preheat oven to 275
Mix the salt, pepper, cumin, chili powder, and cinnamon in a bowl. In a large baking dish, coat the brisket with the spice mixture. in the same bowl, mix the barbecue sauce, hot sauce, vinegar, and water and pour it over the brisket.
Bake the brisket for about 6 hours until it reaches an internal temp of 195 and is very tender but not quite falling apart. Flip it over and baste it with the juices a few times during cooking, and add a little water if it seems too dry. Allow to cool for 20 minutes before slicing.
Toss the onion slices in a bowl with the salt and allow them to sit for 5 to 10 minutes as the salt brings some juices out of the onion.
Add the spices and flour to the onion and toss until the flour is coating the onions.
Heat a thin layer of oil in a large frying pan and add in some of the onions, being careful not to overcrowd the pan. Cook about 5 minutes stirring a few times until brown. Remove from pan on to a paper towel lined plate.
Mix all the slaw ingredients and season with salt and pepper.
Toast the burger buns.
Form the beef into 3 oz thin patties with a slightly larger radius than the buns to allow for shrinkage. Grill the burgers a few minutes on each side to brown and cook to a medium doneness. Add the cheese to each patty after flipping.
Build the burger starting with the bottom bun, some barbecue sauce sauce, 3 slices of brisket, more sauce, two burger patties, more sauce, the slaw, onions straws, and a little more sauce on top. Add the top bun and serve.