Preheat the oven: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish or casserole dish with cooking spray or a little olive oil.

1. Prepare the cauliflower: If using fresh cauliflower, cut it into small florets. Steam or blanch the cauliflower in boiling water for 5-7 minutes until slightly tender. If using frozen cauliflower, simply thaw and drain any excess water. Once cooked, place the cauliflower in the prepared baking dish.
2. Make the creamy sauce: In a medium saucepan over medium heat, combine the cream cheese, sour cream (or Greek yogurt), chicken broth, garlic powder, onion powder, thyme (if using), salt, and pepper. Stir occasionally until the cream cheese melts and the sauce becomes smooth and creamy.
3. Assemble the casserole: Add the shredded chicken to the cauliflower in the baking dish. Pour the creamy sauce over the chicken and cauliflower mixture, stirring gently to coat everything evenly.
4. Add the cheese: Sprinkle the shredded cheddar cheese evenly over the top of the casserole. If desired, top with Parmesan cheese for an extra layer of flavor.
5. Bake the casserole: Place the casserole in the preheated oven and bake for 25-30 minutes, or until the cheese is bubbly and golden brown on top. If you like a crispier top, you can broil the casserole for an additional 2-3 minutes, keeping a close eye on it to prevent burning.
6. Serve and garnish: Once done, remove the casserole from the oven and let it sit for a few minutes before serving. Garnish with fresh parsley, if desired.