1. Heat oil in a large skillet or cast iron. Add sliced onion and garlic, cook until fragrant (3 minutes). Add diced tomatoes, stir. Proceed to add in coconut milk, sour cream (if using) and tomato paste. Give sauce a stir and allow it to cook for about 3 minutes.
2. Add sliced pepper and cod chunks. Season with salt, pepper and red pepper flakes. Cover and allow fish to simmer for 10-12 minutes. About 3/4 of the way carefully turn the cod, if the fish hasn’t been fully immerse in the broth.
3. When done garnish with fresh cilantro, if desired, and serve.