Place the chilli in a small heatproof bowl, pour over boiling water and leave to soak for 20 minutes, turning occasionally, until softened. Drain well. Heat a large, dry, heavy-based frying pan, add the garlic and cook for 2 minutes on each side until browned and soft. Place the rehydrated chilli, garlic, oregano, cumin and tomatoes in a food processor or blender and whizz to a coarse sauce.
Heat the oil in the pan, add the tomato sauce and cook for about 5 minutes until reduced to a thick paste. Pour in the stock and bring to the boil. Add the beans and reduce to a simmer.
Add the mussels and fish and cook for 5–7 minutes until the fish is opaque and the mussels have opened. Discard any mussels that remain closed.
Spoon white rice into serving bowls and ladle over the stew. Sprinkle with coriander and red onion and serve with lime wedges.