Place the chicken breasts in the bottom of the slow cooker and top with the garlic.
In a medium bowl, whisk together the tomato sauce, milk, cornstarch, salt, dried Italian seasoning, and black pepper. Then, pour the mixture over the chicken.
Cook the chicken on low for 3 hours or high for 1 ½ hours (or until the internal temperature reaches 165°F).
Once cooked, stir the fresh basil into the sauce. Serve the chicken over gluten-free pasta and top with additional fresh basil, if desired.
Notes
I like to stir in ½ -1 cup of the pasta cooking water into the sauce and toss the gluten-free spaghetti in the sauce before serving.