In a large food processor, combine the avocados, spring onions, chicken stock, tomato paste, chilli sauce, lime juice and tequila. Reserve a little bit of coriander for garnish, then put the rest into the processor. Process until smooth. If you have an immersion blender, you may do this in a pot or large bowl.
Season with salt and pepper. Transfer to a large bowl, cover and refrigerate for at least 2 hours before serving.
To serve, divide the soup between four chilled bowls. Top with a dollop of sour cream and a sprig of coriander.