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°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.
If you like this slow-cooker recipe, try Slow Cooked Greek-Style Beef Stew, Slow Cooked Creamy Chicken & Wild Rice or Slow-Cooker Braised Pork with Salsa.