Place 16 of the lemon grass stalks in a bowl of water and leave to soak for 1 hour. Chop the remaining 2 stalks.
Put the chicken, chopped lemon grass, garlic, lime leaves and half the soy sauce in a food processor and process until well combined. Divide the mixture into 16 portions and mould each portion around a piece of the soaked lemon grass.
Place on a baking sheet, drizzle with half the oil and cook under a hot grill for 4–5 minutes, turning occasionally, until golden and cooked through.
Heat the remaining oil in a wok or frying pan, add the vegetables and stir-fry for 2–3 minutes until just tender, then add the remaining soy sauce. Serve the stir-fried vegetables with the chicken.