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 tablespoon butter and ⅛ teaspoon salt; set aside.

In a medium saucepan, combine 1 tablespoon butter, the mushrooms, onion and remaining 1 teaspoon 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 tablespoon 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.