Heat oil in a pan and sauté garlic and onions till lightly browned and tender. Add in spices, and fry for a few seconds.
Add in the coconut milk, season with salt and pepper, and let it come to a slight boil.
Add in the the pieces of fish and tomatoes, and let it simmer for another 6-7 minutes till the fish is completely cooked through.
Garnish with coriander leaves and serve with a side of plain rice and a tossed salad.