Place the bacon and onion into a
skillet over medium heat, and cook until the bacon is almost crisp and the onion is beginning to brown, about 10 minutes. Stir the bacon mixture into the sauerkraut. In the same
skillet, brown the kielbasa sausage in the remaining bacon grease until the sausage begins to brown, 10 to 15 minutes; stir into the sauerkraut mixture. Spoon the sauerkraut and sausage mixture into the prepared
baking dish.