1 scallion, cleaned and sliced (reserve some for garnishing)
1/2 cucumber, peeled with seeds removed
2 Tablespoons plain yogurt
1/2 lemon, juiced
fleur de sel, freshly ground pepper
1. Cut the avocado in half. Remove the seed. Scoop out the flesh and place in the blender.
2. Add the chopped scallion. Cut up the cucumber and add to the blender.
3. Add the yogurt and squeeze in the lemon juice. Blend.
Season the mousse with salt and pepper.
Place in a small bowl, sprinkle with the reserved onion and top with a cucumber slice.