Preheat the oven to 400°F (200°C). Wash the beetroots thoroughly and wrap each one in aluminum foil.
Place the wrapped beetroots on a baking tray and roast them in the preheated oven for about 30 minutes, or until they are tender when pierced with a fork.
While the beetroots are roasting, peel and slice the cucumbers into thin rounds. Place them in a mixing bowl.
Chop the red onion and add it to the bowl with the cucumbers. Also, add the chopped parsley.
In a small bowl, whisk together the olive oil, balsamic vinegar, Dijon mustard, salt, and pepper to create the dressing.
Once the beetroots are cooked and cool enough to handle, peel and chop them into bite-sized pieces. Add them to the cucumber mixture.
Pour the dressing over the salad and toss gently to combine all ingredients and coat them evenly.
If desired, crumble feta cheese on top before serving.
Serve the salad in a serving bowl and enjoy!