Preheat oven to 450°.
Cook pasta according to package directions, omitting salt and fat. Drain.
Heat oil in a large nonstick skillet over medium-high heat. Sprinkle turkey with 1/2 teaspoon onion powder, 1/4 teaspoon salt, and 1/8 teaspoon pepper. Add turkey to pan; cook 2 minutes on each side or until done. Remove turkey from pan.
Add 1/4 teaspoon onion powder, sherry, and mushrooms to pan. Cover and cook 4 minutes or until mushrooms are tender.
Combine peas, milk, sour cream, cheese, and soup in a large bowl. Chop turkey. Add 1/4 teaspoon salt, 1/8 teaspoon pepper, pasta, turkey, and mushroom mixture to soup mixture, tossing gently to combine. Spoon mixture into a 13 x 9-inch baking dish coated with cooking spray.
Combine breadcrumbs and butter in a small dish, tossing to combine. Sprinkle breadcrumb mixture over pasta mixture. Bake at 450° for 12 minutes or until bubbly and thoroughly heated.