1.Toss lamb in flour; shake away excess. Heat oil in large saucepan; cook lamb, in batches, until browned all over.
2.Cook onion and garlic in same pan, stirring, until onion softens. Add paste; cook, stirring, until fragrant. Return lamb to pan with the water, undrained tomatoes, sugar and stock; bring to a boil. Reduce heat, simmer, covered, 1½ hours.
3.Add cauliflower, pumpkin and lentils to curry; bring to a boil. Reduce heat, simmer, covered, 15 minutes or until cooked as desired. Remove from heat; stir in coriander.
4.Serve lamb shanks with warmed naan, if desired.