My husband is on Coumadin and cannot have ginger. What would you recommend for a substitution?

Would galangal also react with your husband's medication? (Found at Asian grocers, especially those that focus on SE Asian ingredients)

Ginger would add heat and aromatic - galangal probably best approximates it. If that doesn't work (or isn't worth the effort to track down) you could either leave out entirely or add different aromatics - lemongrass as suggested above, chillies, kaffir lime leaves, etc.

Lemongrass? Tarragon?

Never made this dish, but it sounds good!

However, my father was on coumadin for 20+ years and I often cooked for him. My understanding is the same as drbabs re: supplements or teas. Vitamin K (found in ginger, but also spinach, broccoli, cabbage, etc.) can amplify the effect of anticoagulants, but is okay in small amounts. But definitely ask your husband's doc if it's okay for him.

I think you should check with your husband's doctor about using a little fresh ginger as a flavoring. I think when you read about the interaction of ginger and coumadin, they're talking about ginger as a supplement, which would be in a much higher amount than a little fresh ginger grated over a piece of fish. That said, you could just leave the ginger out--the dish is delicious either way.