If you have a mandolin or blender with a juilienne attachment, slice the kohlrabi and carrot through them. If not, thinly slice and then julienne them by hand.
Mix together the slaw ingredients and then the dressing ingredients in a separate bowl.
Mix the dressing into the slaw when you’re ready to eat and sprinkle the crushed walnuts on top. Keep any leftovers in the fridge.