In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute until fragrant.

Pour in the crushed tomatoes, and then add the chopped Kalamata olives, dried oregano, dried basil, red pepper flakes (if using), salt, and pepper. Stir to combine and let the mixture simmer for about 10 minutes, allowing the flavors to meld.

Carefully place the cod fillets into the sauce, spooning some of the sauce over the top. Cover the skillet and let the cod poach in the simmering sauce for about 8-10 minutes, or until the fish is cooked through and flakes easily with a fork.

Once the cod is cooked, drizzle the fresh lemon juice over the top for added brightness.

Garnish with chopped fresh parsley before serving. This dish pairs beautifully with crusty bread, rice, or a simple green salad.