Place onion in a slow cooker and cover with pork tenderloin.
In a small bowl, whisk together remaining ingredients (honey through lemon juice); pour mixture over tenderloin.
Cover and cook on LOW for 8 to 10 hours.
Notes
SERVING SUGGESTION: Steamed broccoli spears and Cauli-Rice (process cauliflower in a blender or food processor until it resembles grains of rice; steam “rice” till tender; drain; salt and pepper to taste and fluff with a fork).