Add the chicken to the slow cooker and season with the salt, pepper and red pepper flakes.
Next, add the pesto, cream cheese, and cubed butter on top of the chicken.
Cover and cook on low for 6 hours or high for 4 hours.
Shred the chicken with 2 forks, right in the slow cooker. Or remove to a plate if that's easier for you.
Cook the pasta according to the package directions on the stove top to al dente (don't overcook). Add the cooked and drained pasta, heavy whipping cream, and mozzarella cheese to the slow cooker with the chicken and sauce, stir.
Serve immediately with a sprinkle of parmesan cheese and crushed red pepper flakes and enjoy!
Notes
Homemade pesto can be used instead of storebought.
Add any remaining pesto chicken pasta into an airtight container and store in the fridge for up to 4 days. To reheat, add to a skillet over medium heat. You may have to add a bit more liquid (olive oil or chicken stock will work) to recreate the creamy sauce.
Chicken thighs are fine to use instead of chicken breasts.
Any pasta shape can be used, but be sure not to overcook it, or it will fall apart when stirred into the chicken and sauce