Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 10-15 minutes or until tender. Drain and cool to room temperature.
In a small bowl, combine the vinegar, sugar, oil and 1/2 teaspoon oregano; set aside. In a large bowl, combine the mayonnaise, salt and remaining oregano. Add potatoes and toss to coat. Cover and refrigerate until chilled.
Just before serving, toss lettuce with the vinegar mixture; place on a serving platter. Top with potato salad. Garnish with cherry tomatoes if desired.