Mix together the oil, 1 tablespoon of the vinegar, garlic and 1 tablespoon of the tarragon in a bowl. Stir in the chicken breast chunks and marinade for 30 minutes.
Heat the barbecue, or preheat a grill to high. Soak some wooden skewers in cold water for 20-30 minutes.
Thread the marinated chicken and chorizo slices onto wooden skewers. Barbecue or grill for around 10 minutes, or until the chicken is cooked through.
Meanwhile mix the rocket and tomatoes to form a salad.
Mix the mayonnaise with the remaining vinegar and tarragon and season to taste with freshly ground black pepper. Gently stir through the rocket salad.
Remove the chicken and chorizo from the skewers and serve scattered over the salad.