Bake the beetroots in their skins for 60–90 minutes or boil for 40–60 minutes. Cool and peel them.
Peel and core the apples.
Dice the onions finely or slice them thinly. Grate the apples and beetroots on a coarse grater.
Combine all ingredients in a bowl. Add olive oil, lemon juice, sugar, salt, and pepper. Mix well.