Preparing Pan-Seared Mediterranean Cod in Tomato Basil Sauce is a simple yet rewarding process, consisting of the following steps:

1. Heat Oil: In a large skillet, heat 2 tablespoons of olive oil over medium heat.
2. Sauté Onion: Add the diced onion to the skillet and sauté until translucent, about 3-4 minutes.
3. Add Garlic: Stir in the minced garlic and cook for an additional 1 minute, until fragrant.
4. Incorporate Tomatoes: Pour in the can of diced tomatoes (with juices) and stir. Add oregano, red pepper flakes, and season with salt and pepper to taste.
5. Simmer Sauce: Allow the sauce to simmer for 10-15 minutes, stirring occasionally until it thickens slightly.
6. Cook the Cod: Season the cod fillets lightly with salt and pepper. In a separate pan, heat the remaining olive oil over medium-high heat.
7. Pan-Sear Cod: Carefully place the cod fillets in the skillet and sear for about 3-4 minutes per side or until the fish flakes easily with a fork.
8. Combine: Once the cod is cooked, gently add it to the simmering tomato sauce and sprinkle the chopped basil over the top.
9. Heat Together: Let everything heat through for an additional 1-2 minutes, allowing the flavors to meld.
10. Serve: Remove from heat and serve immediately with lemon wedges on the side.

This step-by-step guide will lead you to an incredible execution of Pan-Seared Mediterranean Cod in Tomato Basil Sauce!