Spray a large saucepan with oil and set over a medium heat. Sauté onion for 3 minutes, or until softened. Add garlic, carrot, sweet potato and zucchini; cook, stirring occasionally, for 5 minutes, or until vegetables are hot.
Stir in curry paste; cook, stirring, for 1 minute, or until fragrant. Stir in tomatoes, stock and 2 cups of water; cover and bring to the boil. Reduce heat. Partially cover; simmer, stirring occasionally, for 25 minutes. Stir through the chickpeas and simmer for 10 minutes, or until vegetables are tender.
Stir through coriander. Ladle soup into bowls; top each with a dollop of yoghurt and extra coriander leaves.