Cook pasta according to package directions. Rinse with cold water. Drain completely and transfer to a large bowl. Stir in cucumber, red onion, tomatoes and oregano (or dill).
In a small bowl, whisk mayonnaise, sugar, vinegar, salt and pepper. Mix it with the pasta mixture to coat thoroughly. Taste and adjust seasoning as necessary.
Refrigerate for 30 minutes or more before serving.
Enjoy!