1.In a bowl combine kumara and flour. Toss to coat and season to taste. Shape tablespoons of mixture into flat discs.
2.In a large frying pan, heat half oil and butter together on medium. Pry discs in 2 batches, 1-2 minutes each side, until golden and crisp, adding extra butter and oil as required. Drain on paper towel.
3.In a large bowl combine lentils, tomato, beans, spinach, parsley and onion.
4.Make Dressing; in a small jug, whisk all ingredients together. Season to taste. Drizzle over salad, tossing to coat. Top with rosti to serve.