Warm a pan over a medium heat. Tip in the caraway seeds and toast for 2 mins till popping and fragrant. Pour into a dish for later.
Peel and finely chop the onion. Peel and crush the garlic. Put the pan back over a medium heat. Gloss the pan with 1 tbsp oil. Add the onion, season and cook for 5 mins till softened. Add the garlic and cook for 1 min.
Break the broccoli into small florets. Thinly slice the stalk. Add to the pan. Pour in 800ml boiling water. Bring to a gentle simmer with the lid off. Cook for 10 mins.
Halve the avocado and scoop out the flesh, discarding the stone. Chop into small chunks. Don’t worry if it’s a little firm, it will soften in the hot soup.
Add the spinach to the pan and stir it through to wilt it. Add the avocado. Simmer for 2 mins. Ladle into a blender and blend till smooth and creamy, or use a hand-held blender in the pan.
Zest and juice the lemon. Swirl most of the caraway seeds through the soup, leaving a couple of pinches to garnish. Stir through half of the lemon zest and juice. Taste and season, adding a little more lemon juice to taste. Ladle into warm bowl and garnish with the remaining caraway seeds and lemon zest.