In the meantime, heat about a teaspoon of olive oil (or use cooking spray) in a medium non stick pan over medium heat and cook the endive and asparagus for 2-3 minutes, until just tender. Remove from heat but leave in pan.
Add avocado, yogurt, lemon juice, salt and pepper to the bowl of your food processor and process until smooth.
When pasta is cooked, drain it and add it to your reserved vegetables. Add avocado mixture and chopped walnuts and toss delicately to combine.