Cook pasta according to package directions, omitting salt and fat. Drain and return to pan. Cover and keep warm.
Heat a large nonstick skillet over medium-high heat. Add oil; swirl to coat. Add mushrooms; cook 8 minutes or until browned and tender, stirring occasionally. Stir in sherry, scraping pan to loosen browned bits. Cook 1 minute or until liquid evaporates. Remove mushrooms from pan. Add onion and garlic to pan; sauté over medium heat 4 minutes. Add 1 tablespoon water; cook 1 minute or until tender, stirring constantly.
Place flour in a large saucepan; gradually add vegetable broth and next 4 ingredients (through pepper), stirring with a whisk until blended. Place over medium heat; cook until thick (about 5 minutes), stirring constantly. Add butter, stirring until melted. Add sauce, mushrooms, onion mixture, turkey, peas, and 1/2 cup cheese to pasta, stirring until cheese melts. Pour mixture into a 13 x 9inch glass or ceramic baking dish coated with cooking spray. Sprinkle with remaining 1/2 cup cheese.
Bake, uncovered, at 350° for 25 minutes. Let stand 5 minutes. Garnish with thyme, if desired.
Kids Can Help: Kids can combine the sauce, turkey, peas, onion mixture, and mushrooms with the pasta, and then sprinkle the cheese on top before it bakes.