Peel the beetroots and carrots, then grate them roughly. Finely chop the onion.
Put them in a mixing bowl, add all other ingredients and combine. Cover and rest for an hour in the refrigerator.
Preheat the oven to 180°C.
Remove the mixture from the fridge and form 8 hamburger patties (or 16-20 mini patties). Rest on a tray for 10 minutes.
Heat on spoonful of olive oil in a pan and fry the patties on each side for a couple of minutes until golden brown.
Place them on a lined baking tray and bake in the oven for 15 minutes.
Meanwhile prepare the buns, condiments or side dishes.