Prepare the Baking Dish and Preheat Oven : Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with a bit of vegetable oil to prevent sticking.

Sauté the Onion : Heat the teaspoon of vegetable oil in a small skillet over medium heat. Add the chopped onion and sauté for 3-4 minutes, until softened. Set aside.

Mix the Creamy Base : In a large mixing bowl, combine the cream of chicken soup, sour cream, milk, shredded cheese, ranch dressing & seasoning mix, and black pepper. Stir well until the mixture is smooth and creamy.

Assemble the Casserole : Add the shredded cooked chicken and sautéed onion to the bowl with the creamy mixture, stirring to coat. Pour the chicken mixture into the prepared baking dish, spreading it out evenly. Arrange the frozen tater tots in a single layer over the top of the chicken mixture. Sprinkle the crumbled bacon over the top of the tater tots.

Bake : Bake in the preheated oven for 40-45 minutes, or until the casserole is bubbly and the tater tots are golden brown and crispy.

Garnish and Serve : Remove from the oven and let cool slightly. Garnish with chopped chives for a burst of color and extra flavor. Serve warm and enjoy this creamy, cheesy, bacon-loaded casserole!