Put mussels in a large pot with a lid. Pour 1/4 cup water over all, cover, bring to a boil, then reduce heat to maintain a steady bubble (you will hear it and see some steam escaping). Shake pot now and then.
Meanwhile, combine coconut milk, lime juice, fish sauce, lime zest, and chiles in a large bowl; add bean sprouts, cucumber, scallions, and red pepper.
Mussels will be done in 5 to 10 minutes, or when all or most of the shells have opened. Remove and let cool slightly, reserving cooking liquid. (If there is a great deal, reduce it while you shuck mussels.)
When mussels are cool enough to handle, remove them from their shells and add them to bowl with vegetables and dressing. Add cilantro and as much of the reserved cooking liquid as you need to make mixture saucy. Toss well to combine, adjust seasonings, and serve, or refrigerate up to a few hours.
*There is an excellent tutorial by "The Kitchen"