Season the steak with olive oil and salt and pepper. Set aside while you preheat the grill.
In a bowl combine the chilli, lime juice, sugar, fish sauce and sweet chilli sauce.
In a serving bowl combine the lime leaves, coriander, mint, cucumber, carrot, watercress and tomatoes.
Grill the steak until it is seared on the outside but still pink inside, about 4 minutes a side. Remove from the heat and let rest 5 minutes. Slice and toss with the rest of the salad and the dressing. Serve immediately.