Place The Chicken Into A 3 1/2-Quart Slow Cooker. Top With All But 2 Tablespoons Of The Taco Seasoning. Pour 3 1/2 Cups Of The Stock Over The Chicken. Cover And Cook On Low For 4 To 5 Hours Or Until The Chicken Is Cooked Through. Remove The Chicken To A Cutting Board. Using 2 Forks, Shred The Chicken. Heat The Oven To 350 Degrees F. Heat The Butter In A 3-Quart Saucepan Over Medium Heat. Stir The Remaining Taco Seasoning, Stock And Soup In The Saucepan. Stir In The Chicken. Layer Half Of The Chicken Mixture, Tortillas, And Cheese In A 3-Quart Shallow Baking Dish. Repeat The Layer. Bake For 30 Minutes Or Until The Mixture Is Hot And Bubbling. Serve Over The Rice.