Mix the spices: Combine cumin, turmeric, coriander, fennel, pepper, and salt. Reserve ⅓ for the relish.
Season the cod: Rub 1½ tablespoon lemon juice and ⅔ of the spice mix onto the fish.
Sauté aromatics: Heat ½ tablespoon oil in a skillet. Cook ginger and onions until soft (4–5 minutes).
Bloom the spices: Stir in the reserved spice mix for 30 seconds until fragrant.
Make the relish: Add corn and 1½ tablespoon lemon juice. Cook 3–4 minutes. Remove from pan.
Sear the cod: Add ½ tablespoon oil, then cook cod 2–3 minutes per side until opaque and flaky.
Serve: Plate the cod with the warm corn relish and finish with cilantro.