Heat a pan and add your choice of oil (about 2 tablespoons). Add the diced onions, sliced green chillies, curry leaves, and crushed garlic. Sauté on medium heat until the onions are lightly caramelised.
Add in the turmeric and Kashmiri masala. Let the spices cook down and braise for 2–3 minutes, releasing their full aroma.
While your spices are cooking, boil your eggs if you're using them. Once done, peel and slice them in half.
Add the grated tomatoes to the pan and mix well. Season with salt and balance the acidity with ½ to 1 teaspoon of sugar. If using tamarind, add it now. Let the chutney simmer on low to medium heat for about 10 minutes until it thickens slightly.
Gently add in the cleaned tin fish. Try not to stir too vigorously, just gently coat the fish with the chutney. Pop the lid on and let it warm through for 2–3 minutes.
Add your halved boiled eggs, tucking them into the chutney and spooning a bit of sauce over each one. Cover again for another 2–3 minutes.
Garnish with chopped fresh coriander and remove from heat.