Spray carrots, turnip, and parsnips with olive oil on both sides. Spread on a baking sheet. Roast in an oven at 400 degrees for 30 minutes. Set aside.
Combine barley and broth in an electric pressure cooker. Set on high pressure for 18 minutes. Release pressure manually when done cooking.
Drain excess liquid from the barley, retaining the liquid.
Set pressure cooker to saute. Pour enough of the retained broth into the cooker to cover the bottom of the pot to a depth of 1/2 inch. Saute the mushrooms, adding broth as needed to keep from drying. Allow broth to reduce to a sauce.
Top barley with roasted vegetables and mushrooms. Pour reduced broth over the barley. Salt and pepper to taste.