Heat the oil in a large wok, (you can use a frying pan if you don't own a wok). Stir fry the ginger, lemon grass, chilli and garlic for about 1 minute or until fragrant. Add the pork and cook for about 5 minutes or until it is cooked through.
Remove the pork mixture from the stove and allow to cool slightly. Combine the lime juice, fish sauce and brown sugar. Pour over the pork mixture.
Toss the salad greens, onion, mint and most of coriander leaves, (leave some coriander to garnish), with the pork mixture. Serve the salad in a bowl and garnish with the reserved coriander leaves.