Fry the spring onions in a spray of olive oil until soft. Add the garlic and fry for another minute before tipping in most of the watercress, all the rocket and parsley. Stir though until wilted, then add the vegetable stock. Bring to a simmer and season well. Blend until a stick blender until smooth. Add most of the lemon zest and season with a little lemon juice.
Divide between bowls, then add a tbsp of cashew cream to each bowl. Scatter with more lemon zest and watercress leaves to serve if you like.