Place mushrooms in a small bowl and cover with warm water; let stand for 30 minutes. Combine bulgur with the boiling water in another small bowl and let soak until the bulgur is tender and the water has been absorbed, about 30 minutes. Remove the mushrooms from the liquid; trim stems and coarsely chop caps.

Preheat oven to 350 degrees F. Coat a baking sheet with cooking spray.

Heat oil in a small skillet over medium-low heat and add onion, celery and garlic. Cook, stirring occasionally, until the vegetables are softened, 5 to 7 minutes. Add Worcestershire and cook for 3 minutes, scraping the pan well as the mixture becomes sticky. Add tomatoes, evaporated milk and ketchup; stir to combine. Continue cooking until the mixture is very thick, about 3 minutes. Remove from the heat and let cool.

Whisk egg and egg whites in a large bowl. Add beef, breadcrumbs, the soaked bulgur, the mushrooms and the tomato mixture. Stir in parsley, thyme and salt. Mix gently but thoroughly with your hands.

Mound the meatloaf mixture into a free-form loaf on the prepared baking sheet. Bake until the internal temperature reaches 165 degrees F, 50 to 60 minutes. Let cool for 10 minutes before slicing and serving.

Ingredient note: Bulgur is made by parboiling, drying and coarsely grinding or cracking wheat berries. It simply needs a quick soak in hot water for most uses. Look for it in the natural-foods section of large supermarkets, near other grains, or online at kalustyans.com, lebaneseproducts.com.