Bring a saucepan of water to the boil. Plunge tomatoes into the boiling water for a second or too then immediately remove to a medium bowl of ice water. Drain, then remove skins. Chop and set aside.
Heat olive oil in a frying pan over medium heat, and cook onion until tender. Stir in garlic and oregano. Stir in tomatoes, and cook until softened. Mix in wine, olives, capers, lemon juice and the chopped basil.
Reduce heat, mix in Parmesan cheese and simmer until the mixture is reduced to a thick sauce, about 15 minutes.
Place fish in a shallow baking dish. Cover with the sauce, and top with remaining basil leaves.
Bake in the preheated oven for 12 minutes until fish is easily flaked with a fork.
Altered ingredient amounts.
I followed the advice of other reviewers & cooked the flounder filets seperately (also, there's one person in our house who will only eat plain flounder) and added the sauce to the plate. I also used only half the amount of capers called for (I thought 4 Tbs woulkd be too much), a can of diced tomatoes(drained) and I couldn't get fresh basil so I used dried. The dish came out so good, I was very close to making the same thing for dinner again the next night. We had it with Jasmine rice, steamed summer squash & fresh Italian bread. - 29 Sep 2008