Step 1

Preheat oven to 375°F. Lightly spray a 13- x 9-inch baking dish with cooking spray.

Step 2

Cook pasta in a large Dutch oven according to package directions for al dente. Drain pasta, and set aside. Do not wipe Dutch oven clean.

Step 3

Melt butter in Dutch oven over medium-high, and add chicken, salt, and 1 teaspoon of the lemon pepper. Cook, stirring often, until chicken is beginning to get a little color but is not completely cooked, about 6 minutes. Add onion, celery, and 1 cup of the scallions; cook, stirring often, until vegetables are beginning to soften, about 4 minutes. Add flour, and cook, stirring constantly, 1 minute to blend completely. Gradually stir in milk and cream, gently scraping Dutch oven to release any flour mixture from bottom. Bring mixture to a boil over medium-high. Boil, stirring often, until sauce thickens, about 2 minutes. Remove from heat. Add cheeses, hot sauce, sour cream, cooked and drained pasta, and remaining 1/2 cup chopped scallions, stirring until well combined.

Step 4

Spoon mixture into prepared baking dish; sprinkle with blue cheese. Top with panko, and sprinkle remaining 1/2 teaspoon lemon pepper over panko. Spray lightly with cooking spray.

Step 5

Bake in preheated oven until pasta mixture is bubbly and panko topping is lightly browned, about 15 minutes. Garnish with additional chopped scallions.