Preheat the oven to 200 degrees. Wash the beets thoroughly, wrap them in foil and put them in the oven for one hour. Cut the pumpkin and celery into cubes, and the onion into quarters. Put the vegetables in a baking dish, season with salt, pepper, and drizzle with oil. Bake until soft, about 30 minutes.
Cool the vegetables. Cover the beets with cold water, cool, peel, and cut into small slices. Finely chop the greens. Put the vegetables in a salad bowl, sprinkle with herbs, pour the dressing.