Cut squash in half lengthwise. Remove and discard seeds and membranes. Cut each squash half into 3 wedges. Using a 5- to 6-quart slow cooker place squash and onion. Remove excess fat from chops. Place chops in cooker. Combine in a small bowl the chicken broth, marmalade, mustard, marjoram, and pepper. Pour over mixture in cooker.
Cover and cook on low-heat setting for 5 to 6 hours or on high-heat setting for 2 1/2 to 3 hours.
Remove chops and vegetables to a serving platter, reserving cooking liquid. Cover chops and vegetables with foil to keep warm.
For sauce, strain cooking liquid into a glass measuring cup. Skim off fat. Measure 1 3/4 liquid (add water if necessary to make 1 1/4 cups). Pour liquid into a medium saucepan. Combine in a small bowl cornstarch and water. Stir into liquid in saucepan. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Serve chops and vegetables with sauce.