Nusa Dua is in Dean Street, Soho and is a mostly Thai/Malaysian/vaguely oriental restaurant. For me their particular attraction is the pre-theatre menu for just £6.95 a head before 6PM.
You get a small basket of prawn crackers, a bowl of light vegetable soup, a small starter and a main course with rice or noodles. I think they give you a cup of green tea afterwards but we were in a hurry last time we went so I'm not sure. The options are more limited than those on their standard menu, but there is still plenty of choice including veggie options. The portions aren't huge (my starter was one spring roll) but there is plenty to fill you up. You can always have pudding if you're still peckish ;o)
I've been several times and it's always been good, and it's particularly useful for grabbing a quick bite between work and your evening activities.
The only caveat is the house wine - it's a bit meh.
Between the two of us the meal cost £20 for the meals, three soft drinks and discretionary tip.