Marinade: Stir together the lime juice, cumin, paprika, garlic, salt and pepper in a bowl. Add the fish and toss to coat. Cover and refrigerate at least 20 minutes, up to 24 hours.
Stew: Heat the olive oil in a large saucepan over medium-high heat. Quickly fry the onions in the oil 1 to 2 minutes. Reduce heat to medium. Add the capsicums, fish and diced tomatoes to the saucepan in succeeding layers.
Pour the coconut milk over the mixture. Cover the saucepan and simmer 15 minutes, stirring occasionally. Stir in the coriander and continue cooking until the fish is completely cooked through, another 5 to 10 minutes.