Combine citrus juice, cumin, paprika, garlic, salt and pepper in a large bowl.
Add the fish pieces and mix until all pieces are thoroughly covered in spice mixture.
Cover and refrigerate at least 30 minutes or longer. Overnight works too.
Heat the oil in a large skillet or pot over medium heat.
Add onions and cook until soft, about 2 to 3 minutes.
Add green pepper, tomatoes, and marinated fish.
Add the coconut milk and stir gently until just combined. Cover and simmer 20 minutes.
In the final minutes of simmering, stir in the cilantro. Garnish with cilantro sprigs if desired.