Fill a high-sided skillet with an inch or two of oil, making sure not to fill more than halfway up. Set over moderate heat. Once hot, carefully add a tortilla. Fry one at a time until golden and crispy, about 1 to 2 minutes per side. Transfer to a plate lined with paper towels to soak up the excess oil. Transfer to a wire rack set over a baking sheet, to prevent from getting soggy. While warm, sprinkle with a bit of salt.
Set a large skillet over medium-high heat. Add the bacon and cook until crispy. Use a slotted spoon to transfer the bacon to a plate lined with paper towels; set aside. Drain all but 1 tablespoon of the bacon grease. Add the ground beef and use a wooden spoon to break up the beef. Cook, stirring often, until no longer pink and just starting to brown. Stir in half of the chopped onion (reserving the other half for topping), granulated garlic, granulated onion, cayenne, salt and pepper. Cook until the onions have softened, about 1 to 2 minutes longer. Stir in the crispy bacon, ketchup, mustard and mayo. Cook until warmed through.
To make the sauce, in a small bowl, stir together the mayo, ketchup, mustard, relish, vinegar, cayenne, and a pinch of salt and pepper. This can be made up to 2 days in advance and kept in the fridge until ready to use.
To assemble, spoon the warm beef mixture onto the tostada shells. Top with shredded lettuce, tomatoes, reserved onion, cheese, pickles and the burger sauce. Serve immediately and enjoy!