Lightly coat the interior of a 3.5 to 5-quart slow cooker with cooking spray.

Pour the measured cream of mushroom soup into the prepared slow cooker. Add the chicken stock, garlic powder, salt, and black pepper. Whisk these ingredients together until smoothly blended.

Nestle the chicken breasts into the sauce mixture. Scatter the sliced mushrooms evenly over the chicken.

Secure the lid and set the slow cooker to LOW for 3.5 to 5.5 hours or on HIGH for 1.5 to 2.5 hours. Cook until the chicken is opaque, tender, and cooked through (internal temperature of 165∘F or 74∘C).

Once cooked, carefully transfer the chicken breasts to a clean cutting board to rest for a few minutes.

Meanwhile, prepare the thickening slurry: in a small bowl, whisk the cornstarch with the cold water until no lumps remain. Gently stir this slurry into the sauce in the slow cooker. Replace the lid to allow the sauce to heat and thicken slightly, about 10-15 minutes on low (or if you turned it off, turn to high for a few minutes).

Using two forks, shred the rested chicken to your desired consistency. Introduce the shredded chicken back into the thickened sauce in the slow cooker. Stir gently to combine all ingredients thoroughly.

Keep the dish on the WARM setting until you are ready to serve. This dish is excellent served over cauliflower rice, alongside steamed green beans, or with a fresh side salad for a complete low-carbohydrate, diabetic-friendly meal.