If colcanon had lentils in it,

then it would be something like this. Half an onion, sliced in strips and sauteed. Half a head of cabbage, coarsely shredded. A couple pieces of ginger, a little garlic, a dash of red wine vinegar, a couple small potatoes, cut thin. A cup of lentils. Cover with water and boil into something between stew and soup. Add salt to taste.