Combine barbecue sauce, grated apple and lemon juice in a small bowl; mix well.
Wrap 2 pieces of bacon around each chicken breast. Place chicken breasts in base of crock pot.
Pour barbecue sauce mixture over top of chicken, along with a couple apple slices (optional).
Cover; cook on Low for 8 hours.
Remove chicken from crock pot.
OPTIONAL - Skim fat from sauce. Pour sauce into a small saucepan; bring to a boil. Combine cornstarch and water; whisk until blended. Add cornstarch mixture to sauce; stir until thickened. Serve sauce with chicken.