Grate the frozen chicken breasts into a bowl. Add the egg and panko bread crumbs to the grated chicken, season with salt and pepper, and mix well. Line a 6 x 2-inch bowl with plastic wrap and add the chicken mixture. Firmly press it into the bowl so it takes on the shape of the bowl and then cover it with plastic wrap. Put the bowl in the freezer for about 90 minutes.
Preheat the oven to 325°F. Remove the frozen chicken mass from the plastic wrap and dredge it in egg, flour, and panko bread crumbs. Deep fry the breaded chicken in 300°F oil for 10 minutes and then cook it in the oven for 30 minutes. Cut the chicken nugget bun in half and spread mayonnaise over the bottom half.
Season the ground beef with salt and pepper and form 2 large, flat hamburger patties. Place the 3 red onion slices on top of the first patty, cover it with the second patty, and seal the edges together with your hands to make one stuffed hamburger patty.
Fry the hamburger patty on both sides over medium heat for about 8 minutes. Place the patty on the bottom chicken nugget bun and top with cheese and crispy bacon.
Spread some BBQ sauce on the top half of the chicken nugget bun and place it on top of the burger.