Place cucumbers, onion, and tomatoes in a large mixing bowl.
In a small bowl, whisk together olive oil, red wine vinegar, sugar, salt, and black pepper until the sugar dissolves.
Pour the marinade over the vegetables and toss gently to coat.
Sprinkle fresh dill on top and toss again to combine.
Cover and refrigerate for at least 30 minutes before serving to let the flavors meld.
Serve chilled and enjoy.
