1. Take out the cod fillets and the citrus mixture for 30 minutes at room temperature. Cut the semi-thawed cod fillets into thin slices and let them thaw in the refrigerator.
2. Cut the citrus mixture into small pieces and reserve them in a bowl.
3. Mix olive oil, lemon juice, ginger, shallot, salt, and pepper, then add the citrus and basil.
4. Spread a little of this marinade on 4 flat plates, then place the well-thawed cod slices on top.
5. Drizzle with marinade and serve immediately.