Preheat the oven on 200 degrees C (400 degrees F). Then take beets and wash them. After washing the beets, put them in the baking dish along with ¼ cup of water.
Cover the baking dish and bake it for one hour or until the beets get tender. After that take the baking dish out from the oven and place it aside so it could cool down.
Take apple cider, salt, pepper, vinegar, celery seed and mustard and mix them together to form a mixture.
When the beets cool down, peel and slice them. Then, combine them with the mixture. After mixing, put it in the refrigerator for half an hour at least.
Take salad greens and equally divide them in four salad plates.
Then, take out the beets from the refrigerator after half an hour and drain them in a way that their dressing remains reserve. Set the beets, apple, onion and avocado on the greens in a decorative style to give it an elegant look and drizzle it with reserve dressing.
Lastly sprinkle some nuts on the top of the salad before serving this delicious dish.