In a large pot melt the butter
Add the chopped onions and sauté until slightly golden
Add vegetable stock to the onions and bring just to a boil
Reduce heat and simmer on low, adding the sweet peas
Cook for about four minutes or until tender
Remove from heat and stir in the spinach and mint leaves
Allow to cool and stir in the avocado and the lemon juice
Puree the mixture with an immersion blender until smooth
Season with salt and pepper to taste
Chill completely before serving, at least 1 hour in the fridgeIf desired add garnish before serving.