Heat oil in a pan over medium heat.
Add cumin seeds and let them splutter.
Sauté chopped onion until golden brown.
Stir in ginger-garlic paste and cook for a minute.
Add pureed tomatoes and cook until the oil separates.
Mix in turmeric, red chili powder, and coriander powder.
Pour in the coconut milk and bring to a simmer.
Gently add fish fillets to the sauce.
Cook for about 10-12 minutes until the fish is cooked through.
Garnish with fresh cilantro before serving.