Heat the oil in a wok over a high heat until the oil starts to shimmer. Toss in the garlic, lemon grass, ginger and onion and stir-fry for about 5 minutes.
Add the chicken and stir-fry for 5–7 minutes until the chicken is browned and cooked.
Add the tomatoes, asparagus, shoyu or tamari sauce and black pepper and stir-fry for 2–3 minutes to warm through. Garnish with the Thai basil leaves.