Soak tamarind in hot water 10–15 min.
Heat coconut oil, add fenugreek seeds, then onions. Sauté until golden, add garlic.
Add spice mix and curry leaves, cook 2–3 min.
Add tamarind with soaking water, then fish pieces in a single layer.
Gently coat fish with gravy, pour in the coconut milk, and add chilies.
Cover and simmer 10 minutes on low-medium heat.
To prepare the tempering, heat coconut oil and fry fenugreek, onion, garlic, dried chilies, and curry leaves. Pour over the curry.
Gently shake the pot to mix. Serve hot.