01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to boil. Cook pasta according to package directions until al dente. Drain well and set aside.
03 - Heat a large skillet over medium heat. Add a splash of oil or butter, then sauté diced onion for 3 minutes until softened. Add minced garlic and cook for 1 minute until fragrant.
04 - Stir cooked chicken, crumbled bacon, thawed peas, salt, pepper, smoked paprika, and dried thyme into the skillet with the onions. Remove from heat.
05 - In a large bowl, whisk together sour cream, softened cream cheese, whole milk, and 2 cups shredded cheddar cheese until smooth and creamy.
06 - Add the drained pasta and chicken mixture to the cheese sauce. Stir thoroughly until all ingredients are evenly coated and combined.
07 - Pour the mixture into the prepared 9x13-inch baking dish. Spread evenly with a spatula, ensuring the surface is level.
08 - In a small bowl, combine panko breadcrumbs, melted butter, and remaining 1/2 cup cheddar cheese. Mix until the breadcrumbs are evenly coated.
09 - Sprinkle the breadcrumb-cheese mixture evenly over the top of the casserole, covering the entire surface.
10 - Bake for 25-30 minutes until the casserole is bubbling around the edges and the topping is golden brown and crispy.
11 - Remove from oven and let the casserole rest for 5 minutes. This allows the sauce to set slightly for easier serving.