Combine the curry paste, garlic, soy sauce, brown sugar and lemon grass in a small bowl. Add the chicken, mix well, cover and refrigerate for 1 hour.
Thread the chicken, red onion, red pepper and yellow pepper onto soaked bamboo skewers.
Cook the skewers on a preheated barbecue for 8 minutes, or until the chicken is cooked through and the vegetables are tender. Serve with the dipping sauce.
To prepare the sauce combine all ingredients.