Cook chicken: Preheat oven to 375 F. Place chicken in an oven safe pan. Sprinkle all over both sides with salt and pepper. Add water around chicken, cover pan with foil and bake for 25 – 35 minutes until chicken is cooked through (reached an internal temperature of 165 F). Once cooked, removed from oven, cool and shred together with pan juice. Set aside.
After chicken is cooked, reduce oven heat to 350 F. Coat a 9x9 baking dish with non stick spray and set aside (You can also prepare everything in a Dutch oven, if you prefer).
Add cream cheese, ranch, hot sauce, garlic powder and black pepper to a large sauce pan or Dutch oven and melt over medium heat, stirring frequently. Removed from heat, add shredded chicken, green onion, 1 cup of mozzarella and 1 cup of shredded cheddar, mixing well to combine. Pour ingredients into the prepared pan or, if using a Dutch oven, it can go from stovetop to oven.
Top with remaining cheese and bake for 20 – 30 minutes, until cheese has melted and it begins to bubble.