Preheat oven to 400 degrees F. Position two oven racks in the top and bottom thirds of the oven.Cook pearl barley according to package instructions. Drain and set aside to cool.Wash and trim beets; set greens aside. Place beets in the center of a piece of aluminum foil, two beets per square of foil. Drizzle with about 2 tablespoons olive oil and rub all over beets. Sprinkle with salt and pepper. Gather foil around tops of beets to form a packet, with the opening at the top to prevent leakage. Place packets on a cookie sheet and roast for 50 to 60 minutes or until beets are fork tender. Carefully open tops of foil to release steam, and let cool for about 10 minutes. When beets are cool enough to handle, rub skins off using a paper towel. Slice into 3/8-inch slices and then cut slices into cubes.While beets are roasting, bring a large pot of water to a boil. Cut thick stems out of beet greens and discard. Blanch greens for 30 seconds until bright green, then transfer to an ice bath. Drain, squeezing out as much liquid as possible from the greens, and place in the bowl of your food processor along with basil, parsley, garlic, pine nuts, honey, orange zest, vinegar, and salt. Pulse 3 or 4 times to chop. Scrape down sides as needed, then add olive oil and pulse a few more times to combine.Toss mushrooms with 1/4 cup olive oil, fresh thyme, and a generous pinch of salt and pepper. Spread in a single layer on a foil-lined baking sheet lightly coated with cooking spray. Roast for 20 to 25 minutes, stirring once, until mushrooms are golden brown and nearly crispy.To assemble, toss barley with about 2/3 of pesto mixture. Divide among serving bowls. Top with cubed beets, roasted mushrooms, crumbled goat cheese, and a sprinkle of pine nuts if desired. Serve warm or at room temperature with remaining pesto alongside.