Put the pineapple juice into a bowl. Stir the ketchup and spices into the juice, add the chicken and toss together. Leave to marinate for at least 30 minutes.
Meanwhile, to make the salsa, finely chop the pineapple rings and put in a bowl with the tomatoes and sweetcorn. Add the chilli (if using), ginger and half the coriander and toss together.
Thread the pepper chunks on to 12 wooden or metal skewers, alternating with the chicken pieces. Sprinkle the skewers with the remaining chopped coriander. Grill the skewers under a preheated hot grill for 10–12 minutes, turning several times until well browned and the chicken is cooked through.
Serve the skewers with brown rice and spoonfuls of the salsa.