You can use any small- to medium-sized long-stemmed mushrooms, but I prefer buna-shimeji or bunapi-shimeji.
Use any type of lettuce you like. Use cooking spray in place of oil, if you prefer. The wakame can be fresh or dried, soaked, and drained.
Optional ingredients include grated cucumber, carrot, beet, chopped spring onion, toasted sesame seeds, pepitas, soft tofu, tuna, egg, sesame oil, etc.