Prepare the Soup:
Heat oil in a large saucepan and sauté onions until soft. Stir in the cumin, garlic, chili and lemon zest and cook until fragrant.
Add the potato and stock and season to taste. Bring to the boil, reduce the heat, cover and simmer for 20-30 minutes until potato is tender.
Introduce the quinoa:
Purée soup and bring back up to the boil, add the quinoa and extra water, reduce the heat, cover and simmer for 15-20 minutes until quinoa is cooked.
Prepare the garnish:
Heat the oil in a small frying pan and sauté the garlic until it just starts to change colour. Add the cumin and cook until it starts to bubble.
Stir in the coriander and cook for a few seconds until the coriander starts to wilt, then pour the garnish into the soup.
Stir in the garnish, check and adjust the seasoning. Serve with a good squeeze of lemon juice.