Sprinkle ribs with Cajun seasoning; rub in with your fingers. Cut ribs into single rib portions. Place ribs in a 3 1/2- to 4-quart slow cooker.
In a medium bowl combine chili sauce, onion, serrano pepper, tapioca, lemon peel, lemon juice, and hot pepper sauce. Pour sauce over ribs.
Cover and cook on low-heat setting for 5 to 6 hours or on high-heat setting for 2 1/2 to 3 hours. Serve immediately or keep covered on warm or low heat setting for up to 2 hours. (Remove any bones without meat.) If desired, sprinkle with parsley.