Trim fat from roast. In small bowl, combine garlic powder, ginger, thyme, and pepper. Rub spice mixture over entire roast. In large skillet, brown roast on all sides in hot oil. Drain.
Transfer meat to slow cooker. Combine chicken broth, sugar, lemon juice, soy sauce and orange peel. Pour over roast.
Cover and cook on low for 8-10 hours or on high for 4-5 hours.
Transfer roast to serving platter, keep warm. For sauce, pour juices into glass measuring cup, skim fat. Add water to equal 2 cups. Transfer to saucepan. Combine cornstarch and orange juice, stir into juices in saucepan. Cook and stir until thickened and bubbly. Cook and stir 2 minutes more. Serve sauce with meat.