Mix together the garlic, olive oil and vinegar in a non-metallic bowl, add the chicken and coat in the marinade. Cover and leave to marinate in the refrigerator for at least 30 minutes.
Cook the rice in a saucepan of boiling water according to the pack instructions. Drain well and leave to cool, then mix with the peppers, spring onions, tomatoes, rocket and goats' cheese in a large bowl.
Whisk together the dressing ingredients in a bowl and stir into the rice salad. Spoon the salad on to 4 serving plates.
Heat a griddle pan until hot and cook the chicken for 3–4 minutes on each side until cooked through. Immediately before serving, slice the griddled chicken and arrange on top of the salad.