Preheat oven to 350 degrees.
Peel and diced red potatoes, while bringing a large pot of water to a rapid boil.
Add potatoes to water and boil for 15-20 minutes or until potatoes are tender.
In a large mixing bowl add potatoes, 1/2 cup of milk and season with salt and pepper to your taste. Beat the potatoes, milk and seasonings until they become creamy and smooth. Add more or less milk, depending on the way you like.
There should be about 6 cups of mashed potatoes, place on the bottom of a 9x13 pan or casserole dish.
If you are using a rotisserie chicken, shred or coarsely chop all the meat from the chicken, removing skin and bones.
If you are boiling the chicken breasts, bring a large pot of water to a boil. Once boiling, add chicken breast and boil until chicken is fully cooked; around 15-25 minutes. Time varies depending on the size of the chicken breast.
Once cooked, remove from water and shred or coarsely chop.
Top the mashed potatoes in the pan with the chicken.
In a large glass measuring cup (4 cups) or small mixing bowl, add both cans of cream of chicken. Add milk to one of the empty cream of chicken cans (full). Add the milk to the bowl along with 1/2 teaspoon granulated garlic, 1/2 teaspoon pepper, and 1/2 teaspoon salt. Mix well.
Pour "gravy" evenly over the chicken/potatoes. Cover pan with foil and place in the oven for 30-35 minutes, until mixture is hot and gravy is bubbling.
Remove from oven and serve immediately. Top with cheese if so desired, this is a family favorite in our home.