Pat the shrimp and fish dry with paper towels. Keep the seafood refrigerated while you prepare the sauce.
Heat the neutral oil and dendê palm oil, if using, in a large deep skillet or Dutch oven over medium heat. If you do not have dendê oil, use 2 tablespoons (30 mL) neutral oil total. Add the onion and bell pepper and cook, stirring occasionally, until softened, about 5 minutes.
Stir in the garlic, tomato paste, and cayenne. Cook for 30 seconds, just until fragrant.
Pour in the coconut milk and broth. Whisk in the bread crumbs, peanut butter, and ground peanuts until no lumps remain. Bring the mixture to a gentle simmer, then cook for 5 to 7 minutes, stirring often, until thickened and creamy.
For a smoother vatapá, use an immersion blender to briefly blend the sauce directly in the pot. Alternatively, leave it slightly textured. Keep the heat at a gentle simmer; do not boil vigorously.
Add the shrimp and fish in an even layer. Cover and cook gently for 4 to 6 minutes, turning the fish pieces once if needed, until the shrimp are opaque and the fish flakes easily. Avoid stirring hard so the fish stays in pieces.
Remove the pot from the heat. Stir in the lime juice, salt, black pepper, and cilantro. Taste and adjust the salt, lime, or cayenne. Serve hot with white rice and extra cilantro, if desired.