1 jar (25.5 oz) tomato basil pasta sauce (or make your own)
3/4 cup water
2 cups shredded mozzarella cheese (8 oz)
In a medium bowl, mix chicken, ricotta cheese, garlic salt, and red pepper flakes; stir in 1/4 cup of the basil. Spoon into quart-sized resealable food-storage plastic bag. Cut 3/4 inch tip off bag. Pipe filling into manicotti shells.
Spray 5-quart slow cooker with cooking spray. In a medium bowl, mix pasta sauce and water. Spread about 1/3 of the sauce mixture in slow cooker. Place 7 of the filled manicotti shells in pasta sauce. Sprinkle with 1 cup of the mozzarella cheese. Spoon another 1/3 of the sauce mixture over shells. Top with remaining 7 filled manicotti shells; sprinkle with remaining 1 cup mozzarella cheese. Top with remaining 1/3 of sauce mixture.
Cover; cook to 3 hours on High heat setting or until shells are tender. Serve with remaining 1/4 cup basil.