Place chicken in the slow cooker.
Sprinkle with onion soup mix.
Top chicken with cream of chicken soup.
Cover slow cooker and cook on low for 6 hours or high for 3.
Shred the chicken in the slow cooker.
Stir in sour cream and Velveeta cheese.
Prepare rice according to package directions.
Stir into cheese and chicken mixture.
Top with shredded cheddar if desired, serve!!