Place squash on a baking sheet, and bake at 400° for 1 hour or until tender; let cool. Peel squash, and cut in half lengthwise; discard seeds and membrane. Mash pulp. Combine mashed squash, 1/4 cup water, truffle oil, and vinegar in a blender, and process until smooth; set aside.
Place barley in a large nonstick skillet, and cook over medium heat 4 minutes or until toasted. Set aside.
Bring 3 1/2 cups water to a boil in a large saucepan. Add rices; cover, reduce heat, and simmer 10 minutes. Stir in toasted barley; cover and simmer 40 minutes or until grains are tender. Set aside.
Heat 1 tablespoon olive oil in skillet over medium-high heat. Add mushroom caps, leek, carrot, celery, and garlic; sauté 5 minutes. Add 1/4 cup water, and cook 1 minute. Add wine, and cook 2 minutes or until liquid evaporates. Stir in squash mixture, grains, green peas, and next 6 ingredients (green peas through thyme); cook 2 minutes or until thoroughly heated. Remove from heat; stir in cheese, salt, and pepper. Sprinkle with pumpkinseed kernels.