Heat 2 Tbsp olive oil in a medium cast iron dutch oven (I like Le Creuset but any heavy bottom deep pan will do) and sauté leek for 2-3 minutes, while stirring occasionally.
Add barley to the pan and stir to coat well with the sautéed leeks, continue to cook for an additional 2-3 minutes.
Add water to the pan and continue to cook, covered for 15 minutes.
Turn off the heat and keep lid on for 5 more minutes.
Transfer to a medium bowl and add the diced pear, and walnuts and stir again gently; let it cool for 5-10 minutes.
Meanwhile, place all dressing ingredients in a small container and whisk briskly to blend well.
Add the dressing to the barley salad and stir well.