1.Heat oil in a large saucepan over moderately low heat. Add onion; cook and stir for 5 minutes or until soft.
2.Add garlic and curry powder. Cook and stir for 1 minute or until fragrant. Add tomato and stock. Bring to the boil. Reduce heat.
3.Add kumara; simmer, uncovered, for 10 minutes. Add cauliflower and zucchini. Simmer, stirring occasionally, for 5 minutes or until vegetables are tender.
4.Add lentils; cook and stir for 5 minutes or until heated. Season with salt and pepper.
5.Toast naan; brush with combined butter and coriander. Cut into wedges. Ladle hot soup into serving bowls. Top with yoghurt, if liked. Serve with naan.
Sprinkle naan with caraway seeds or cumin, if liked.