Preheat Oven To Broil. In A Shallow Bowl, Whisk Together The Olive Oil And Vinegar. Marinate The Tomatoes In The Mixture, Stirring Occasionally. Meanwhile, In A Small Bowl, Combine Mayonnaise, Parsley, Oregano, Black Pepper And 4 Teaspoons Parmesan Cheese. Spread Mixture On Each Slice Of Toasted Bread. Place Marinated Tomatoes On 2 Slices And Sprinkle With Remaining Parmesan Cheese. Place On A Baking Sheet And Broil For 5 Minutes, Or Until Cheese Turns Golden Brown. Serve Immediately, Open Faced Or Closed.