If your chicken is not yet cooked, bring a large pot of water to a boil over high heat. Add the chicken breasts to the pot and return to a boil. Remove from heat and cover with a tight-fitting lid. Allow your chicken to poach, covered, for approximately 25 minutes. When fully cooked, remove from the pot and allow to rest until cool enough to handle
After your chicken has been cooked and shredded, heat the cream cheese, ranch dressing, hot sauce, black pepper, and garlic powder in a small pot over medium-low heat. Whisk constantly until combined and creamy, then remove from heat.
Stir in the green onion, shredded chicken, one cup of the shredded cheddar cheese, and one cup of the shredded mozzarella cheese. Transfer the mixture to a baking pan and sprinkle with the remaining shredded cheese.