Take 1 medium-sized beetroot, cut off the tail and top, add salt, pour vegetable oil (I used walnut oil). Wrap the beets in foil and bake in the oven for 35 minutes at 200C. Meanwhile, peel and slice the carrots, parsnips and sweet potatoes into fairly large pieces. Cut small red onions into quarters. Add salt to the vegetables, pour vegetable oil and send them to the baking tray where our beets are baked. Bake the vegetables together for another 35 minutes.
For the dressing, mix the olive oil, mustard, balsamic and lemon juice.
Peel the baked beets, cut them, and mix them with the dressing. Add the remaining vegetables, lettuce leaves and mix. When serving, sprinkle with feta and chopped walnuts.