Preheat oven to 350°.
Cut each squash in half lengthwise, and discard seeds and membranes. Place squash, cut sides down, on a baking sheet, and bake at 350° for 35 minutes or until tender. Cool to touch. Scoop out pulp, leaving a 1/4-inch shell. Mash pulp to measure 2 cups; set aside.
Heat oil in a large saucepan over medium heat until hot. Add bell pepper and onions; sauté 5 minutes. Add broth and sage; bring to a boil. Stir in barley; return to a boil. Cover, reduce heat, and simmer 15 minutes. Uncover; cook 10 minutes or until most of liquid is absorbed. Remove from heat; stir in mashed squash, parsley, salt, and pepper. Divide mixture evenly among squash halves. Place on a baking sheet; bake at 350° for 15 minutes. Sprinkle evenly with cheese; bake an additional 5 minutes or until cheese melts.