Preheat oven to 375 degrees.
Coat a large rimmed baking sheet or roasting pan with cooking spray.
Heat oil in a large skillet over medium heat.
Add celery and onion.
Cook, stirring often, until softened, 2 to 3 minutes.
Add cremini mushrooms.
Cook, stirring occasionally, until they give off their moisture and it mostly evaporates, about 5 minutes.
Pour into a large bowl and cool for 10 minutes.
Stir in egg, turkey, ground porcini, breadcrumbs, tomato paste, Worcestershire sauce, thyme, salt and pepper until well combined, taking care not to over mix.
Use a scant 3/4-cup to form an oval loaf about 4 inches long and 21/2 inches wide.
Transfer to the prepared pan.
Make 5 more loaves with the remaining mixture.
Bake the loaves until lightly browned and an instant-read thermometer inserted into the center of one registers 165 degrees, 35 to 40 minutes.
Slice and serve.
Ready in 1 1/2 hour.