Heat coconut oil in a large pot over medium heat. Add cumin seeds, toast 30 seconds until fragrant.
Add onion, cook 5 minutes until softened.
Add garlic and ginger, cook 1 minute.
Stir in curry powder and turmeric, cook 1 minute.
Add tomatoes, cook 5 minutes until broken down.
Pour in coconut milk, bring to a gentle simmer, and cook 8 minutes to let the sauce develop.
Add fish chunks, simmer gently 8–10 minutes until just cooked through.
Season with salt, top with cilantro, and serve hot.