Heat the oil in a pan. Add the onion and cook until soft. Add the white wine and boil for 2 minutes. Add the sauerkraut, cumin, caraway and juniper berries. Cut the potatoes in half and add. Cover and simmer for 15 minutes, adding a little water if necessary. Crisp the pancetta in the oven or under the grill. Skin the trout and break into large pieces. Place the trout on the sauerkraut, cover, and heat through for 3 minutes. To serve, top with crisp pancetta, scatter with parsley and serve with a dollop of grain mustard.