Marinated cucumber salad

Ingredients:
3 medium cucumbers, peeled and sliced 1/4 inch thick
1 medium onion, sliced and cut into rings
3 medium tomatoes, cut into slices
1/2 cup vinegar
1/4 cup erythritol
1 glass of water
2 teaspoons of salt
1 teaspoon fresh coarsely ground black pepper
1/4 cup oil
1 teaspoon chopped fresh mint (optional)