1. Heat 1 Tbs. oil in medium saucepan over medium-high heat. Add barley, and cook 2 to 3 minutes, or until slightly toasted. Pour in 21/4 cups water, and bring to a simmer. Cover, reduce heat to low, and cook 45 to 55 minutes, or until liquid is absorbed and grains are cooked. (If barley is not completely cooked, add a little more water and continue simmering until tender.) Pour barley out onto cooking-spray-coated baking sheet, and let cool to room temperature. Season with salt and pepper, if desired.
2. Preheat oven to 425°F. Line second baking sheet with parchment paper, or coat with cooking spray. Toss squash with 1 Tbs. oil on baking sheet until evenly coated, and season with salt and pepper, if desired. Roast 35 to 40 minutes, or until tender, stirring occasionally.
3. Heat remaining 1 Tbs. oil in large nonstick skillet over medium-high heat. Add onion, and cook 7 to 9 minutes, or until translucent. Add red pepper flakes, and cook 1 minute more. Add barley, and cook 3 to 5 minutes, or until warmed through. Stir in roasted squash and parsley, and cook 2 minutes more. Remove from heat; stir in pomegranate seeds and pistachios. Serve warm or at room temperature.