Peel and quarter the parsnips, carrots and beets. Peel the potatoes and halve or quarter them as well. Put everything in a bowl.
Rub the peel of the orange, then squeeze out the juice. Add both to the vegetables. Mix everything with the olive oil, sugar, salt, pepper and chilli flakes.
Preheat the oven to 180 ° C (top / bottom heat). Place the vegetables on the deep baking sheet and cook in the oven for about 1 hour.