Cut the fish into cubes. Heat half of the oil in a pan and sear the fish, flipping the pieces halfway to ensure they are evenly cooked.
Remove the fish from pan and set aside.
In the same pan, heat the rest of the oil, then add the cumin seeds and let them crackle.
Add the onion and crushed garlic and saute for a couple of minutes until the onions turn slightly brown and the raw smell of garlic goes away.
Add the chopped tomato and cook for a few more minutes. Keep stirring and press it against the bottom and sides of the pan to squish and mash it properly.
Add the spices (salt, cayenne, turmeric, and coriander powder) and mix. Let it cook for one more minute. Avoid pepper if you're cooking for kids.
Add the coconut milk, mix well, and bring the mixture to a boil. Reduce the heat and simmer for 2 minutes.
If necessary, add some water and cook for a bit longer.
Put the fish pieces in the curry and remove the pan from the flame.
Serve with boiled rice or roti/naan. This curry also goes well with white bread.