How to Make It
Place oven rack in middle position. Preheat broiler to LOW. Lightly coat a 9-x 13-inch baking dish with cooking spray.
Cook pasta according to package directions. Drain, reserving 1/2 cup cooking water. Set aside.
Melt butter in a large skillet over medium-low. Add flour and cook, whisking constantly, until bubbling, about 2 minutes. Increase heat to medium; slowly whisk in milk. Cook, stirring occasionally with a wooden spoon, until sauce thickens, 5 to 6 minutes. Add cheese and salt and cook, whisking constantly, until smooth, about 2 minutes.
Remove mixture from heat. Stir in chicken, basil, parsley, chives, lemon juice, and cooked pasta. Stir in reserved cooking water as needed to create a creamy sauce. Spoon mixture into prepared baking dish.
Transfer to oven and broil until warmed through, about 4 minutes. Garnish with additional basil, parsley, and chives. Serve immediately.