Peel and cube beets and place in aluminum foil. Drizzle olive oil over and season with a pinch of sea salt and pepper. Wrap the beets up and roast in a preheated 400°F oven for 45 minutes, or until they are soft.

While beets are roasting, slice cucumber in half lengthwise and use a spoon to scoop out the seeds. Then slice the cucumber crosswise into ½" c-shaped slices and place in a bowl. Slice onion into thin rounds and add to the cucumbers. Pour ½ cup of white vinegar over and set aside to pickle/marinate while the beets are cooking.

Once beets are done, place beets in a bowl while still warm and add balsamic vinegar, toss to coat and set aside.

In a small bowl, combine minced shallot and remaining teaspoon of vinegar. Add sour cream, mayonnaise, horseradish, dill, salt and pepper and whisk together until smooth. Scatter leafy greens on a large platter. Drain the vinegar off the beets, cucumbers and onions and arrange the vegetables over the greens. Drizzle creamy dressing over and sprinkle top with chopped walnuts, crumbled feta cheese and additional sprigs of dill. Alternatively, serve the dressing in a dish on the side for everyone to help themselves.