Preheat oven to 425°F.

Cook the chicken in a separate pan until fully cooked. Let it cool for a few minutes, then shred it with a mixer or forks.

In a small saucepan over low heat, melt the butter.

Whisk in the flour, then season with salt and pepper to taste.

Slowly whisk in the milk, pouring a little at a time. Continue whisking until the mixture becomes creamy and smooth.

Add the ranch dressing to the sauce and mix until fully combined.

Spray a 9x13-inch baking dish with nonstick cooking spray.

Add a layer of shredded chicken to the bottom of the baking dish.

Pour the creamy ranch sauce over the chicken.

Sprinkle half of the shredded cheddar cheese over the sauce.

Arrange the frozen tater tots evenly over the top.

Bake uncovered for 20 minutes, or until the tater tots are golden and crispy.

While the casserole bakes, crumble the cooked bacon and set it aside.

Remove the casserole from the oven and top with the remaining cheddar cheese and crumbled bacon.

Return to the oven and bake for another 5 minutes, or until the cheese is melted and bubbly.

Remove from the oven and let the casserole cool for a few minutes before serving.