Combine 1 (14 1/4-ounce) can fat-free, reduced-sodium chicken broth, 1/4 cup water, and 1/2 teaspoon curry powder in a medium saucepan; bring to a boil. Stir in 1 (10-ounce) package couscous; cover, remove from heat, and let stand 5 minutes. Stir in 2 tablespoons chopped walnuts and 1/2 cup sliced green onions; fluff couscous with a fork.