Heat the oil in a flameproof casserole, add the onion and cook over a medium heat for 5 minutes until lightly browned. Stir in the garlic, beetroot, kidney beans, chilli flakes and spices, then add the tomatoes, stock, vinegar, sugar and plenty of salt and pepper.
Bring to the boil, then cover and transfer to a preheated oven, 180°C (350°F), Gas Mark 4, for 1½ hours or until the beetroot is tender.
Meanwhile, make the salsa. Mix all the salsa ingredients together in a bowl, then spoon into a serving dish, cover and chill in the refrigerator.
Spoon the brown rice into bowls and top with the chilli and spoonfuls of the salsa. Finish with a dollop of soured cream garnished with the chopped mint leaves.