Put flour, salt, garlic powder, and black pepper into a large, sealable plastic bag. Seal the bag and shake to mix. Add beef cubes to the bag, seal again, and shake to coat beef in the flour mixture.
Heat olive oil in a large skillet over medium heat. Cook beef in hot oil until completely browned on all sides, 7 to 10 minutes. Mix onion with the beef cubes; cook and stir until the onions are translucent, 5 to 7 minutes.
Pour the tomato juice into the skillet; add mushrooms and stir. Place a cover on the skillet, reduce heat to low, and simmer the mixture until the beef is completely tender, about 1 hour.
Stir sour cream into the beef mixture until the sauce is smooth and even in color; add lemon juice and stir.