Trim excess fat from roast. Sprinkle roast with salt, pepper and garlic powder. Spread mustard over roast; place in a large Dutch oven. Cover and bake at 325 degrees for about 2 1/2 hours or until meat thermometer registers 170 degrees. Drain Mandarin oranges, reserving liquid. Set oranges aside. Combine liquid and remaining ingredients except onion and green pepper; cook over medium heat, stirring constantly, until smooth and thickened. Remove from heat; stir in oranges, onion and green pepper. Spoon sauce over roast. Bake uncovered at 400 degrees for 30 minutes, basting occasionally. Slice pork and serve with warm pan drippings. Serves 10.