Preheat oven to 425 degrees F. Coat a 3-quart baking dish with cooking spray.Advertisement
Cook fettuccine in boiling salted water until al dente, about 8 minutes. Drain and refresh under cold running water. Drain and set aside.
Meanwhile, heat oil in a large skillet over medium heat. Add leeks and cook, stirring, until lightly browned, 6 to 8 minutes. Add mushrooms and 1/2 teaspoon rosemary; cook, stirring, until softened, about 5 minutes. Add flour and cook, stirring, for 1 minute. Add broth and milk; bring to a boil, stirring, until slightly thickened, about 4 minutes more. Remove from heat and stir in chicken. Season with lemon juice, salt and pepper.
Gently mix the cooked fettuccine into chicken mixture and spoon into prepared baking dish.
Combine Parmesan, breadcrumbs, lemon zest, parsley and the remaining 1/2 teaspoon rosemary in a small bowl. Season with salt and pepper. Sprinkle the mixture over the casserole.
Bake casserole for 20 to 30 minutes, or until bubbling. Let stand for 5 minutes before serving.
Make Ahead Tip: Prepare through Step 5. The casserole will keep, covered, in the refrigerator for up to 2 days.
2 starch, 2 1/2 vegetable, 2 lean meat