Prepare the Crock Pot: Lightly grease the inside of your slow cooker with butter or non-stick cooking spray. This is a crucial step to prevent the rice from sticking to the bottom and sides.
Combine Ingredients: Add the cubed chicken, minced garlic, chopped onion, salt, pepper, uncooked brown rice, chicken broth, and cream of chicken soup to the prepared crock pot.
Mix Thoroughly: Stir all the ingredients together until everything is well combined. Ensure the rice is fully submerged in the liquid to allow it to cook evenly.
Slow Cook: Secure the lid on the crock pot and cook on the HIGH setting for 3.5 to 4 hours, or on the LOW setting for 6-7 hours. Avoid lifting the lid while it's cooking, as this releases heat and can extend the cooking time.
Check for Doneness: After the 3-hour mark on high (or 6 hours on low), check to see if the rice is tender and has absorbed most of the liquid. The chicken should be cooked through and tender.
Melt the Cheese: Once the chicken and rice are cooked, turn off the crock pot. Stir in the shredded cheddar cheese until it's incorporated. Place the lid back on for another 5-10 minutes to allow the cheese to melt completely into the dish, creating a gooey, cheesy sauce.
Rest and Serve: Let the dish rest for a few minutes before serving. This will allow the sauce to thicken slightly. Serve warm, garnished with fresh parsley if desired.