Lightly spray a Dutch oven with vegetable cooking spray and heat over medium high heat, add ground beef and cook until no longer pink, about 2 minutes, stir to crumble beef.
Place beef in a strainer and rinse under hot water to remove excess fat, drain well and set aside.
Wipe grease out of Dutch oven with paper towel, then again spray lightly with cooking spray (do not spray over flame). Sauté onions until translucent, about 3 minutes, stir often.
Add in potatoes, mushrooms, water, beef bouillon, oregano, and pepper. Raise heat to high and bring to a boil. Lower heat, cover, and simmer until potatoes are tender, about 10 minutes; remove from heat.
Stir in beef, salt, and blue cheese; let sit 2 minutes for flavors to combine.