Butterfly each pork piece, open it flat and pound it between parchment to an even 1/4-inch thickness.
Season the pork with the salt, coat it in flour, dip it in beaten egg and press it into the combined panko and cracker crumbs.
Heat the oil in a deep skillet to 350°F, keeping the skillet no more than halfway full.
Fry 2 cutlets at a time for 2 to 3 minutes per side, maintaining 340°F to 350°F, until crisp and the centers reach 145°F.
Drain the cutlets on a wire rack for 3 minutes so the bottom crust stays firm.
Spread the buns with mustard and add one pork cutlet, 4 pickle chips and sliced onion to each.
Close the sandwiches without trimming the crisp edges that extend beyond the buns.