01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with cooking spray or butter.
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 1 minute until fragrant.
04 - Stir in cooked chicken, crumbled bacon, thawed peas, salt, black pepper, smoked paprika, and dried thyme. Remove from heat.
05 - In a large bowl, whisk together sour cream, softened cream cheese, whole milk, and 2 cups shredded cheddar until smooth and creamy.
06 - Add drained pasta and chicken mixture to the cheese sauce. Stir thoroughly until all components are evenly coated.
07 - Pour mixture into prepared baking dish. Spread evenly with a spatula, ensuring surface is level.
08 - In a small bowl, combine panko breadcrumbs, melted butter, and remaining 1/2 cup cheddar cheese. Mix until breadcrumbs are evenly coated.
09 - Sprinkle breadcrumb mixture evenly over casserole. Bake for 25-30 minutes until cheese is bubbling and topping is golden brown.
10 - Remove from oven and let casserole rest for 5 minutes before serving to allow layers to set.