Heat half of the oil in large saucepan; cook garlic and sliced onion, stirring, until onion softens. Add garam masala; cook, stirring, 1 minute.
Stir in undrained tomatoes, potato, carrot and the water; bring to a boil. Reduce heat, simmer, covered, 10 minutes. Add zucchini and capsicum; simmer, covered, 10 minutes or until vegetables are tender.
Meanwhile, heat remaining oil in medium saucepan; cook chopped onion, stirring, until soft. Add rice and spices; cook, stirring, until fragrant.
Stir in the extra water and sultanas; bring to a boil. Reduce heat, simmer, covered, about 15 minutes or until rice is just tender and water is absorbed.
Place half of the rice mixture in 2-litre (8-cup) serving dish; top with vegetable mixture then remaining rice mixture. Serve with yogurt, if desired.