01 -  Preheat oven to 190°C. Lightly grease a 23x33 cm baking dish. 
 02 -  In a large bowl, combine sour cream, whole milk, ranch dressing mix, black pepper, and garlic powder. Whisk until smooth. 
 03 -  Fold in the shredded chicken, crumbled bacon (reserving a small amount for topping), half of the shredded cheddar cheese, and mixed vegetables if using. Stir to evenly distribute. 
 04 -  Spread the prepared chicken mixture evenly in the greased baking dish. 
 05 -  Arrange the frozen tater tots in a single layer over the chicken mixture. 
 06 -  Sprinkle the remaining cheddar cheese and reserved bacon evenly over the tater tots. 
 07 -  Bake uncovered for 40–45 minutes, or until the tater tots are golden and the filling is bubbling. 
 08 -  Allow to stand for 5 minutes before serving. Garnish with sliced green onions if desired.