Wash and dry your cucumbers. Slice them thinly into half-moons, depending on your preference. If you're using larger cucumbers with lots of seeds, scoop them out to prevent the salad from getting watery. If you have time, salt them and let them sit in a colander for 20/30 minutes to draw some of the moisture out. Pat them dry with kitchen paper or squeeze them gently. Then rinse.
Take your cooked beets and slice them into thin wedges.
Peel and thinly slice a small red onion. You can soak the slices in cold water for 5-10 minutes to mellow the bite, then drain and pat dry.
Make the Balsamic Vinaigrette
In a small bowl, whisk together balsamic vinegar, mustard and a pinch of salt. Then add olive oil and maple syrup and mix to combine. Taste and adjust the seasoning as needed. You can also blend the dressing if you prefer a smoother texture.
Assemble the Salad
Place the cucumbers, beets, and red onion slices into a large bowl or serving platter. Drizzle the vinaigrette evenly over the salad and toss gently to coat everything without breaking the beets.
Top with chopped walnuts right before serving. If you'd like, you can also add some chopped fresh herbs like parsley, basil, or mint for a little extra color and freshness.
Chill and Serve
Let the salad chill for 10-15 minutes before serving to allow the flavors to meld. Serve cold or at room temperature.