For the macaroni: Stir the mustard, paprika, cayenne, white pepper and salt into half of the bechamel. Bring to a boil, and then remove from the heat. Stir in the mixed cheeses and mozzarella until smooth, and then stir in the scallions and tomatoes.
For the burgers: Form the beef into 4 equal patties and sprinkle them with the blackening seasoning. Grill the burgers to your preferred doneness.
For frying the macaroni and assembly: Meanwhile, fill a pot halfway with oil, and heat to 350 to 375 degrees F. Scoop large balls of macaroni using a scoop or melon-baller. Coat in the flour, then dip in the egg wash, and then finally the panko. Deep-fry the balls until the coating is firm.
Toast the hamburger buns and distribute the bacon, dill pickle chips and spicy grilled onions evenly between them, on the bottom half of each bun. Next, place a patty, followed by a macaroni ball on each. Finish with a ladle of the reserved bechamel sauce on top, before putting the top half of the bun on and squishing it down slightly.