Preheat your oven to 400°F. While it heats, thaw your frozen vegetables if not already done, then drain them thoroughly in a colander—I squeeze them gently in a clean kitchen towel to remove excess moisture, which prevents the casserole from becoming watery. Crush the Ritz crackers into small, bite-sized crumbs and set aside.

In a large mixing bowl, combine the hash browns, shredded rotisserie chicken, bacon bits, 1 cup cheddar cheese, drained vegetables, cream of chicken soup, milk, thyme, and onion powder. Stir everything together until the ingredients are evenly distributed and the soup creates a binding sauce. I find it helpful to break up any clumps of hash browns as I mix to ensure they distribute evenly throughout.

Transfer the casserole mixture into a greased 9x13 inch baking dish, spreading it into an even layer. In a small bowl, combine the crushed Ritz cracker crumbs from Step 1 with the remaining 1/2 cup cheddar cheese, mixing until the cheese is distributed throughout. Sprinkle this mixture evenly over the top of the casserole to create an even golden crust.

Cover the casserole tightly with aluminum foil and bake for 30 minutes. The foil traps steam and prevents the crackers from browning too quickly, allowing the center to cook through evenly. Remove the foil and bake for an additional 15 minutes uncovered, until the cracker topping turns golden brown and the edges of the casserole begin to bubble.

Remove the casserole from the oven and let it rest for 10-15 minutes before serving. This resting period allows the hot cream sauce to set slightly, making the casserole easier to portion and helping the flavors meld together. The top will continue to crisp as it cools slightly.