Preheat your oven to 375°F (190°C) and grease a 9x13-inch casserole dish.
In a large mixing bowl, combine the cooked shredded chicken with the Alfredo sauce, sour cream, garlic powder, salt, pepper, and frozen peas. Stir until well mixed.
Pour the creamy chicken mixture into your prepared casserole dish and spread it out evenly.
Arrange the frozen tater tots in a single layer over the top of your casserole mixture.
Place your assembled casserole in the preheated oven and bake for about 30 minutes or until the tater tots are golden brown and crispy on top.
Sprinkle shredded mozzarella cheese generously over your hot casserole and return it to the oven for another 10 minutes or until melted and bubbly.