Marinate the fish for 1 hour in half the lime juice.
Pat dry and lightly brown over high heat in the oil in a large pot.
Add the vegetables, herbs and spices.
Saute briefly and when glassy add the tomato paste
Stir, and add the shellfish stock and bring to a boil.
Remove the fish and let rest on a plate, continue to boil the stock.
After stock has reduced by 1/3, add the coconut milk and simmer until soup has thickened.
Add the shrimp and cover, cooking for a minute or so to cook shrimp through.
Add the fish and mussels back to the pot, cook until mussels have opened.
Season with salt and lime juice, swirl in the cashew butter and serve.