Put chicken tenders, peppers and onions in crockpot. Sprinkle with ground pepper. Cook on high for 4-5 hrs. or on low for 7-8hrs. Break up, or shred with a fork. Whisk together chicken stock and cornstarch. Heat over med. heat until thickened and bubbly. Remove from heat and stir in cream or milk. Add to chicken in crockpot and stir to combine. Salt to taste, if desired. Serve over rice.