Stir in the diced tomatoes, anchovies, olives, capers, and oregano. Bring the mixture to a simmer and cook for about 5-7 minutes, allowing the flavors to meld.
Season the fish fillets with salt and pepper. Gently nestle the fillets into the sauce, spooning some of the sauce over the top. Cover the skillet and cook for 8-10 minutes, or until the fish is cooked through and flakes easily with a fork.
Remove from heat and garnish with fresh parsley. Serve with lemon wedges on the side.
Notes
For a vegetarian option, substitute the fish with firm tofu and adjust cooking time accordingly.
Add a handful of fresh spinach or kale to the sauce during the last few minutes of cooking for extra nutrients and color.