Peel the sweet potatoes and cut into bite-sized cubes. Peel the onions, quarter them and cut into fine strips.
Mix together with about 3 tablespoons of olive oil, the rosemary needles, a lot of salt and the roughly broken walnut halves in an ovenproof pan. Put top / bottom heat in the oven at 200 ° C, everything is nicely roasted after 25 - 30 minutes.
Allow to cool and mix with the red cabbage or radicchio grated into fine strips, the finely plucked mint leaves, chilli powder, apple cider vinegar and possibly walnut oil.
Let it steep briefly and ideally serve it lukewarm.