1. Heat the oil over medium-high flame in a large pot.
2.  Season the fish with salt and pepper.
3. Sear the fish fillets on both sides - do not cook through.
4. Reduce the heat to medium and add the onions and pepper. Sauté until the onion is translucent.
5. Add the garlic and sauté for 1-2 minutes more.
6.  Add the tomatoes, coconut milk, garam masala or curry powder, tamarind paste or lemon juice, salt and pepper. Bring to a boil, then reduce heat to low and simmer for 6-8 minutes.
7. Add the fish fillets, cover and continue to simmer for 5-10 minutes until the fish is cooked through.
8. Serve with rice, ugali, boiled potatoes, boiled cassava or chapatti.
   Note:

You can substitute fish with shrimp. (You do not have to sear the shrimp)