Cook noodles according to package directions; drain and set aside.
Meanwhile, heat oven to 425°F. In a bowl, combine bread crumbs, ¼ cup cheese, 3 tbsp butter and ⅛ tsp salt; set aside.
In a medium saucepan, combine 1 tbsp butter, the mushrooms, onion and remaining 1 tsp salt. Cover and cook over medium-high heat 3 min. Uncover and cook, stirring, 3 min more; transfer to a bowl. Toss in turkey and peas; set aside.
For sauce, in a medium saucepan, whisk together broth, flour and remaining 2 tbsp butter, bring to a boil. Reduce heat and simmer, whisking constantly, until thickened, 4 to 5 min; remove from heat. Stir in remaining ½ cup cheese, the lemon juice and thyme. Salt and pepper to taste.
In a 13-by-9-inch baking dish, combine sauce, turkey mixture and noodles; top with breadcrumb mixture. Bake until golden and bubbling, 13 to 15 min. Serve warm.
My take on this bake combines all the good stuff with a lightly creamy sauce made from broth and a hit of Parmesan for intense flavor. And of course the crunchy, buttery crumbs on top.