Place onions in a 5- to 6-quart slow cooker. Place beef on top of onions. In a bowl combine wine, tomato paste, vinegar, cinnamon, rosemary, allspice, salt, and crushed red pepper; pour over beef.
Cover and cook on low-heat setting for 6 hours or on high-heat setting for 3 hours. Adjust low-heat setting to high-heat setting. Stir in squash and quince. Cover and cook 1-1/2 to 2 hours more or until squash is tender. If using apples, add to cooker the last 1/2 hour of cooking. Remove and discard cinnamon. Serve pot roast with couscous and juices. Makes 8 servings.
Stove top instructions: Set onions aside to add later. In a 4- to 5- quart Dutch oven, brown beef one third at a time, in 2 tablespoons hot olive or cooking oil. Transfer beef to platter; drain fat and return beef to Dutch oven. Increase wine to 1-1/2 cups and vinegar to 1/3 cup. Stir wine, tomato paste, vinegar, cinnamon, rosemary, allspice, salt, and red pepper into meat. Bring to boiling. Reduce heat and simmer, covered, for 1-1/4 hours. Add onions, squash, and quince, if using. Return to boiling. Reduce heat. Simmer, covered, 30 minutes more or until quince and vegetables are tender. If using apples, add the last 10 minutes of cooking. Remove; discard cinnamon. Serve as above.
Tip: If using apples instead of quince, choose a firm cooking apple such as Granny Smith, Fuji, or Gala.