Serve this with a chunk of French Bread to soak up the leftover broth!
In a heavy bottom pot over medium-low heat, sweat the onions, garlic, and ginger in olive oil until fragrant, about 5 minutes.
Add the curry paste and cook, stirring, until softened, about 1 minute.
Add the coconut milk and water and raise the heat medium-high. Bring just to a boil, stirring to blend all of the ingredients.
Add the mussels and cover the pot. Cook until the mussels open, about 5-7 minutes.
Divide the mussels evenly among two bowls. Discard any mussels that fail to open. Spoon the remaining cooking liquid over the mussels.
Garnish with chopped green onion and cilantro, if desired.