01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Cook pasta in salted boiling water according to package directions until al dente. Drain well and set aside.
03 - In a large skillet over medium heat, sauté diced onion in oil or butter for 3 minutes until softened. Add minced garlic and cook 1 minute until fragrant.
04 - Add cooked chicken, crumbled bacon, thawed peas, salt, pepper, smoked paprika, and dried thyme to the skillet. Stir well and remove from heat.
05 - In a large bowl, whisk together sour cream, softened cream cheese, whole milk, and 2 cups shredded cheddar cheese until completely smooth and creamy.
06 - Add drained pasta and chicken mixture to the cheese sauce. Stir until all ingredients are evenly coated and combined.
07 - Pour the mixture into the prepared baking dish and spread into an even layer with a spatula.
08 - In a small bowl, combine panko breadcrumbs, melted butter, and remaining ½ cup shredded cheddar cheese. Mix until evenly distributed.
09 - Sprinkle the breadcrumb mixture evenly over the casserole. Bake for 25-30 minutes until the cheese is bubbling and the top is golden brown.
10 - Remove from oven and let casserole rest for 5 minutes before serving to allow the sauce to set slightly.