In a dry, heavy pot over low heat, cook onions alone, stirring often, 15 minutes until deeply softened. Do not add fat yet.
Add niter kibbeh, garlic, and ginger. Cook 3 minutes until fragrant.
Stir in berbere, cook 2 minutes to bloom the spices.
Add tomato paste, cook 1 minute.
Pour in broth, bring to a simmer, and cook 5 minutes to let the sauce develop.
Add fish chunks, nestling them into the sauce. Simmer gently, uncovered, 8–10 minutes until just cooked through.
Season with salt and serve hot.