Preheat your oven to 400°F.
In a large mixing bowl, combine thawed hash browns, cooked chicken, bacon bits, 1 cup of shredded cheddar cheese, thawed mixed vegetables, cream of chicken soup, milk, and dried thyme.
Stir until all ingredients are well coated.
Grease a 7×11-inch baking dish with cooking spray or oil.
Spread the hash brown mixture evenly into the prepared dish.
In a small bowl, crush the Ritz crackers and mix with the remaining 1/2 cup of cheddar cheese.
Sprinkle the cracker and cheese topping evenly over the casserole.
Cover with foil and bake for 30 minutes.
Remove foil and bake for another 15 minutes, until the top is golden and bubbling.
Let the casserole rest for 10–15 minutes before serving.