To make herb puree, squeeze juice from lemon. Use a small food processor to puree the juice, coriander, mint and sugar.
Bring potatoes and salted water to the boil and cook for 8-10 minutes until tender. Drain well.
Heat oil in same stockpot over a medium to high heat. Return potatoes with white onion bases, chickpeas and curry powder. Cook, stirring occasionally, until hot. Season. Stir in onion tops. Cover to keep warm.
Meanwhile, toss zucchini and capsicum with olive oil. Season.
Heat an oiled grill plate over a medium to high heat. Add vegetables and cook for about 3 to 5 minutes, turning occasionally, or until tender.
Serve potato mixture and vegetables topped with herb puree.