Wash, peel (if desired), and thinly slice the cucumbers. Cook the beets (roasting, boiling, or steaming are all good options) until tender, then thinly slice them. Thinly slice the red onion and chop the fresh dill.
In a small bowl, whisk together the olive oil, apple cider vinegar, honey (or maple syrup), Dijon mustard, salt, and pepper until well combined.
In a large bowl, combine the sliced cucumbers, beets, and red onion. Pour the dressing over the salad and gently toss to coat. Add the chopped dill and toss again.
For the best flavor, refrigerate the salad for at least 15 minutes before serving to allow the flavors to meld. Serve chilled.
Notes
For a vegan version, use maple syrup instead of honey. You can also add feta cheese for a richer flavor, if not vegan.