Spray inside of slow cooker with cooking spray. Place chicken breasts in slow cooker. combine pineapple syrup, broth, vinegar, brown sugar, garlic, and soy sauce in small saucepan. Cook over medium heat, stirring frequently until sugar dissolves. Pour mixture over chicken. Cover and cook on HIGH heat for 1 hour. Add pineapple chunks, onion, bell pepper; cover and cook on LOW for 6-8 hours. Combine cornstarch and water in a small bowl and mix until smooth. Add mixture to slow cooker and stir to mix. Cover and cook on LOW for 30 minutes.