Heat the olive oil in a large pot over medium heat. Add the onion, garlic, and red bell pepper. Cook for 5 minutes until the vegetables soften.
Stir in the chopped tomatoes and cook for another 3 minutes until they begin to break down.
Pour in the coconut milk and add the sweet potato cubes. Season with salt and black pepper. Bring the mixture to a gentle simmer and cook for 10 minutes.
Add the halibut chunks to the pot. Cover and simmer for 8 minutes until the fish is opaque and flakes easily.
Remove the pot from the heat and stir in the lime juice. Taste and adjust seasoning if needed.
While the stew rests, toast the cassava flour in a dry skillet over low heat for 2 to 3 minutes, stirring often until it turns lightly golden.
Ladle the stew into bowls and sprinkle the toasted cassava flour and chopped cilantro over each serving.