Preheat the oven to 230°C.
Cook the onions, garlic, and ginger in oil in a casserole dish until soft.
Add fish, curry leaves, and 500ml of water to the pan and bring to a simmer.
Bake in the oven for 5 to 6 minutes until the fish is cooked through.
Remove the fish and set aside in a deep dish to keep warm.
Beat eggs, rice flour, sugar, vinegar, coriander, and mint in a bowl until smooth.
Whisk the hot cooking liquor into the egg mixture and return the whole mixture to the pan.
Stir constantly over low heat until thickened without allowing it to boil.
Whisk in ground cumin, green chillies, and tomatoes.
Combine the sauce and fish together and serve immediately.