Trim fat from meat. Cut meat into 1-inch pieces. In a 3-1/2- to 4-1/2-quart slow cooker combine meat, squash, onions, and garlic. Stir in broth, tomato sauce, Worcestershire sauce, dry mustard, the 1/4 teaspoon black pepper, and the allspice.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours.
If using low-heat setting, turn to high-heat setting. In a small bowl combine cold water and cornstarch. Stir cornstarch mixture and frozen green beans into meat mixture. Cover and cook about 15 minutes more or until thickened. If desired, sprinkle each serving with freshly ground black pepper.