Note: You can substitute 2 cups of cooked chopped turkey for the chicken, omitting the marinade and the simmer in step 4.
1. Combine chicken and soy sauce in zipper-lock bag and refrigerate for 30 minutes to 1 hour. Pulse bread, 2 tablespoons Parmesan, 1/4 teaspoon salt, and 1/4 teaspoon pepper in food processor until finely ground, 8 to 10 pulses.
2. Meanwhile, adjust oven rack to upper-middle position and heat oven to 400 degrees. Bring 2 quarts water to boil in large saucepan. Add pasta and 1-1/2 teaspoons salt and cook, stirring often, until just al dente. Reserve 1/2 cup cooking water, then drain pasta and return it to saucepan. Toast flour in 12-inch skillet over medium heat, stirring constantly, until just beginning to brown, about 5 minutes. Whisk flour into reserved cooking water; set aside.
3. Melt butter in now-empty skillet over medium-high heat. Add mushrooms, onion, remaining 1/2 teaspoon salt, and remaining ½ teaspoon pepper and cook until browned, 6 to 8 minutes. Stir in peas and add mixture to saucepan with pasta.
4. Add broth and sherry to now-empty skillet, scraping up browned bits. Stir in reserved flour mixture, cream cheese, and remaining 5 tablespoons Parmesan and bring to boil, whisking until smooth. Add chicken and simmer until exterior of chicken is opaque, about 1 minute. Add chicken mixture to pasta mixture and toss until combined. Scrape into 8-inch-square baking dish and top with bread crumb mixture. Bake until golden brown, 12 to 14 minutes. Let cool on wire rack for 10 minutes. Serve.