Mix the watercress and garlic into the butter and season with plenty of ground black pepper and a little salt. Use your fingers to push a little of the butter under the skin of each chicken breast. Place in a shallow dish, cover with clingfilm and chill for up to 4 hours if time permits.

To cook, place the chicken over hot coals or under a pre-heated grill and cook for 20-25 mins, turning occasionally until the chicken is cooked through and the skin brown and crisp. Serve on a bed of sliced tomatoes with watercress salad and lemon wedges.