Make the marinade by whisking together soy sauce, sesame oil, honey, rice vinegar, garlic, and ginger until well combined.
Marinate the fish by placing cod in a shallow dish or resealable bag and pouring the marinade over the fish. Let it sit for 15–30 minutes.
Cook the cod by baking: Preheat your oven to 400°F (200°C), line a baking dish with parchment paper, and bake marinated cod fillets for 12–15 minutes until the fish flakes easily.
Cook the cod by pan-searing: Heat oil in a skillet over medium heat, add cod fillets, and cook for about 3–4 minutes on each side while spooning extra marinade over top.
Optional glaze preparation: Pour leftover marinade into a saucepan, bring to a simmer, and stir in cornstarch mixed with water until it thickens.
Serve by spooning sauce over cooked fish fillets and garnishing with green onions and sesame seeds. Pair with rice, sweet potatoes, or steamed vegetables.