Bring a large pot of water to a boil over high heat. Add the chicken breasts and return to a boil. Remove the pot from the heat, cover it with a tight-fitting lid and let the chicken poach for about 25 minutes, until the thickest part reaches 165°F on a food thermometer. Take the chicken out, let it cool until you can handle it, then shred it. This time is not counted in the total. Skip this step if you use about 4 cups of cooked rotisserie chicken.

Heat the oven to 350°F and spray a 9x9-inch baking pan (or one of about that size) with nonstick cooking spray.

In a medium saucepot over medium-low heat, add the cubed cream cheese, ranch dressing, hot sauce, black pepper and garlic powder. Whisk constantly until the cream cheese has dissolved into the ranch and hot sauce, then take the pot off the heat.

Add the shredded chicken, green onion, 1 cup of the mozzarella and 1 cup of the cheddar to the pot and mix well. Spread the mixture in the prepared pan and top it with the remaining mozzarella and cheddar.

Bake for about 20 to 30 minutes, until the cheese has melted, the sides bubble and the center of the dip reaches 165°F. Then set the oven to broil and cook for 2 to 3 minutes more, until the top is golden brown, and take it out right away.

Serve hot with tortilla chips, vegetable sticks or crackers.