Heat the coconut oil in a large saucepan with a lid over a low heat until melted. Gently fry the onions, garlic, ginger and celery together for 10 minutes until softened, stirring occasionally.
Meanwhile peel the squash, half, scoop out the seeds and roughly chop the flesh.
Add the squash to the pan then cover with the broth. Put the lid on and simmer until tender, about 20 minutes.
Meanwhile, finely chop the coriander leaves and mix in a small bowl with the lemon zest, garlic and extra virgin olive oil. Season to taste.
Blend the soup in batches with lemon juice, tamari and the coriander stems until smooth. Taste for seasoning (tamari is salty so you’ll need less salt).
Serve each bowl of soup with a drizzle of the coriander oil.