Fry the smoked bacon together with the sauerkraut.
Form burger patties using the bratwurst filling (appx. ½ lb. per patty) and grill for about 5 minutes per side (either on the grill or on a pan on the stove).
Halve the pretzel buns sandwich style and lightly grill the inside.
Lay the burger patties on the bottom part of the bun. Drain the heated sauerkraut and place on top of the patty with small pieces of bacon. Top with a tablespoon of roasted onion.