Preheat the oven to 425°F (218°C) and lightly grease a 9x13 inch baking dish with non-stick spray.
In a large mixing bowl, combine the cooked chicken, alfredo sauce, milk, minced garlic, oregano, and black pepper. Stir until the chicken is evenly coated.
Spread the chicken mixture in an even layer across the bottom of the prepared baking dish.
Sprinkle 1 cup of the shredded mozzarella cheese over the chicken mixture.
Arrange the frozen tater tots in a single, tight layer over the cheese and chicken base.
Bake in the preheated oven for 35 minutes, or until the tater tots are golden and crispy.
Remove the dish from the oven and sprinkle the remaining 1 cup of mozzarella and the parmesan cheese over the tots.
Return to the oven for 5 to 10 minutes until the cheese is fully melted and bubbling.
Garnish with fresh parsley and allow the casserole to set for 5 minutes before serving.