Combine onion, ground coriander, chili powder, black pepper, garlic, salt, and 2 tablespoons of oil to make a paste.
Liberally smear paste over fish fillets, refrigerate, covered for about an hour to marinade.
When ready to prepare, dip the fillets into the combination of cornmeal and flour.
In a large frying pan over medium-high heat, heat 2 tablespoons of oil until very hot. Place two pieces of fish at a time in oil. Fry, turning once, until golden brown and cooked completely.