"This is a unique green dip. The dip can be prepared well in advance and stores well. It is especially good with carrots. Cooking the avocado and adding lemon juice keeps the dip from turning brown. Store dip in a covered container in the fridge."
Heat olive oil in a skillet over medium heat; cook and stir leek until lightly browned, 5 to 10 minutes. Add avocado and horseradish; cook, mashing avocado with a wooden spoon, until heated through, 2 to 3 minutes. Stir lemon juice and salt into avocado-leek mixture.
Blend avocado-leek mixture in a blender until desired consistency is reached.