Place potatoes, carrots, and beets into a large pot and cover with water; bring to a boil and turn off heat. Allow pot to sit on burner until potato mixture cools, 1 to 2 hours.
Place onion in a large bowl and cover with vinegar; set aside.
Peel and chop potatoes, carrots, and beets; add to onion mixture. Mix peas, sunflower seed oil, dill, sea salt, and black pepper into potato mixture and stir well. Cover bowl with plastic wrap and refrigerate, 4 hours to overnight.