Cook spaghetti to desired doneness as directed on package. Drain; cover to keep warm.
Meanwhile, in blender container or food processor bowl with metal blade, combine roasted peppers, milk, flour and salt; blend until smooth.
Sprinkle chicken evenly with garlic-pepper blend. Spray large nonstick skillet with nonstick cooking spray. Heat over medium-high heat until hot. Add chicken; cover and cook 4 to 5 minutes on each side or until browned, fork-tender and juices run clear. Remove chicken from skillet; cover to keep warm.
Add roasted pepper mixture to skillet; cook over medium heat until thickened, stirring constantly. Stir in oil. Serve sauce over chicken and spaghetti.