Lightly coat a 3 1/2- or 4-quart slow cooker with cooking spray. Lightly coat a large nonstick skillet with cooking spray. Heat the skillet over medium-high heat. Add chicken; cook about 2 minutes or until light brown on both sides, turning once.
Place sweet peppers in prepared cooker. Top with chicken. Sprinkle with rosemary. Pour spaghetti sauce over chicken.
Cover and cook on low-heat setting for 6 1/2 to 7 hours or on high-heat setting for 3 1/4 to 3 1/2 hours.
Preheat broiler. Line a baking sheet with foil; set aside. Using a slotted spoon transfer peppers and chicken to a medium bowl, reserving cooking juices. Using two forks pull chicken apart into coarse shreds. Add olives to chicken. In a small bowl combine mozzarella cheese, basil, and Parmesan cheese.
Place bread on prepared baking sheet. Broil 4 to 5 inches from the heat for 1 to 2 minutes or until toasted. Turn over bread slices. Top each slice with some of the chicken mixture; drizzle each with about 1 tablespoon of the cooking juices. Sprinkle each with cheese mixture. Broil 1 to 2 minutes more or until toasted and cheese is melted.