In a small bowl, combine olive oil, balsamic vinegar, and dried oregano. Season with salt and pepper. Whisk until blended and let rest.

Peel the cucumber and create ridges with a fork. Slice thinly and dice into bite-sized pieces.

In a large mixing bowl, add prepared cucumber and quartered cherry tomatoes. If using, add finely chopped red onion and mix gently.

Incorporate fresh mozzarella into the mixture. Stir gently to keep the mozzarella intact.

Pour the dressing over the salad and gently toss to coat every piece.

Let the salad sit for at least 10 minutes at room temperature before serving to enhance flavor.