Combine broth, water, and 1/4 teaspoon salt in a large saucepan; bring to a boil. Stir in quinoa. Cover, reduce heat, and simmer 15 minutes or until liquid is absorbed. Stir in 3 tablespoons parsley, 1 1/2 teaspoons oil, and 1/8 teaspoon black pepper. Remove from heat; keep warm.
Heat remaining 1 1/2 teaspoons oil in a medium nonstick skillet over medium-high heat. Add leek; sauté 6 minutes or until wilted. Add mushroom caps, bell pepper, and wine; cook 2 minutes or until vegetables are tender. Stir in remaining 1/4 teaspoon salt and 1/8 teaspoon black pepper. Place 1 cup quinoa in each of 4 shallow bowls; top each with 1 1/4 cups vegetable mixture and 2 tablespoons walnuts.