Prepare the aromatics by finely chopping the onions, grating the ginger, and mincing the garlic.
Heat olive oil in a large, heavy-bottomed saucepan over medium heat.
Add the curry leaves and fry for 1 minute until fragrant.
Stir in the ginger, garlic, and onions.
Sauté for 3 minutes until the onions are soft and translucent.
Add all the ground spices: turmeric, coriander, cumin, chili powder, and fenugreek.
Cook for 2 minutes, stirring constantly to toast them.
Pour in the unsweetened coconut milk and stir until the sauce is smooth and uniform in color.
Gently add the cod pieces, chopped green chilies, and chopped tomato to the simmering sauce.
Reduce heat to medium-low and simmer uncovered for 10-12 minutes, until the fish is opaque and flakes easily.
Stir in the salt, adjust to your taste, and serve warm.
Simmer, Don't Boil: Keep the heat on a medium-low simmer after adding the coconut milk.
Boiling can cause the sauce to separate and lose its creamy texture.