Place the fish and shrimp in a medium-size bowl and toss with the lime juice, 1 tablespoon of the olive oil, half of the garlic, 1/4 teaspoon of the salt, and the black pepper. Allow to marinate as you prepare the remaining ingredients.
Heat the remaining 2 tablespoons of oil in a large pot over medium heat. Add the onion and the bell peppers and cook until they have softened, about 10 minutes.
Add remaining garlic, paprika, and red pepper flakes, and cook, stirring, for 30 seconds. Then, stir in the tomatoes and the scallions and the remaining 1/2 teaspoon of salt.
Gently nestle the fish and shrimp into the vegetable mixture, then pour the coconut milk over everything.
Bring to a gentle boil, then reduce the heat to medium-low. Cover the pan and simmer until the shrimp is fully cooked and the fish flakes easily with a fork, about 6 more minutes.
Stir in the cilantro. Serve with a squeeze of fresh lime juice.
Notes
The stew will keep in an airtight container in the refrigerator for up to 2 days.