Peel the beets and celeriac and slice them. Make sure the slices are all the same size. Marinate in olive oil, salt and pepper. Cook the vegetables, arranged by variety, sous-vide for 1 hour at 80 ℃. Light the barbecue and heat it to a temperature of 120 ℃. Slide the vegetables in alternating order onto the skewer, brush lightly with the Marinade for chicken and grill for 30 minutes. Cut the little gems in two and grill them on the barbecue too. Lacquer the skewer with Bresc Plum and ginger glaze just before serving. Heat the pitas briefly on the barbecue. Slice the vegetables on the skewer and serve with the pitas. Garnish with the grilled little gem and finish off with the Chunky salsa and flat-leaved parsley.