Slice the onion, lemongrass, mushrooms, garlic, and ginger thin. The lemongrass should be paper thin, a mandolin helps. Sautee in the butter. Add the wine and citrus juice and add the mussels in an insert so they can steam. When the mussels have opened, remove and pour into a bowl. Add all remaining ingredients to the pot of liquid and mix until combined. Pour over the mussels. Best served with bread.