In a large bowl, whisk together the crushed garlic, olive oil, oregano, lemon juice, ouzo (if using), salt, and black pepper. Add the cod fillets, ensuring they are well-coated in the marinade. Cover and let marinate in the refrigerator for at least 1 hour.
Preheat your oven to 350°F (175°C). Lightly grease a baking dish with nonstick cooking spray.
Transfer the marinated cod fillets to the prepared baking dish. Sprinkle the finely chopped red onion and kalamata olives evenly over the fish.
Bake for 25 to 30 minutes, or until the fish is cooked through and flakes easily with a fork. The cod should be tender, juicy, and slightly golden.
Serve hot, ideally with a side of Kaniwa tabbouli or a fresh Greek salad for an authentic Mediterranean experience.