Prepare the soup by placing the avocado in a food processor with the lemon juice, cold vegetable stock, celery and olive oil. Blend until you have a smooth, creamy soup. Season to taste and add a little water if it needs to be thinner in texture. Season and transfer to a bowl.
Drop the reserved avocado stones into the soup (to prevent the soup browning), cover and chill until ready to serve. When ready to serve, pour into chilled glasses and arrange some diced red pepper on top along with some black poppy seeds. Garnish the soup with the pea shoots and serve.