Place the fish in a large nonreactive mixing bowl, add the lime juice, and set aside to marinate while you proceed with the recipe.
Heat a large saute pan over medium- high heat, and add the olive oil. Once it is hot, add the onions and cayenne peppers and saute, stirring often, until the onions are translucent, 3 to 4 minutes. Add the garlic and saute for 30 seconds. Add the tomato paste, diced tomatoes, stock, and 1 teaspoon of the salt, and stir well to incorporate. Bring the mixture to a boil. Season the fish with the remaining teaspoon of salt. Then add the fish (with the lime juice) and the coconut milk. Stir to combine, and bring the liquid to a boil. Cover the pan, reduce the heat to medium-low, and cook until the flesh of the fish starts to flake, about 10 minutes.
Remove the cover, sprinkle the cilantro over the fish, and serve accompanied by steamed white rice.
Yield: 6 to 8 servings