Squeeze the juice of a lime into a shallow dish, then add the soy sauce, oil, garlic, honey, half the chopped chilli and salt and pepper to season. Stir well. Add the chicken and turn to coat. Marinate in the refrigerator for at least 30 minutes or overnight if time permits.
Preheat a grill to a moderate heat. To make the fruity salsa, combine the pineapple with the grated zest and juice of the second lime, the red onion, the rest of the chopped chilli and the mint in a bowl. Season to taste, then set aside.
Lift the chicken from the marinade and place on the grill rack. Grill for 12–15 minutes, turning and basting with the marinade, until the juices run clear when the chicken is pierced with a skewer.
Transfer the chicken to a board and cut diagonally into strips. Divide the spinach leaves among four plates, arrange the chicken on top and scatter with the tomatoes. Spoon the salsa over the top and serve immediately.