In food processor, pulse onion and mushrooms to coarse texture. Set aside.
In large frying pan, brown ground beef. Drain fat. Set aside.
In same frying pan, heat oil. Add mushroom mixture and sauté 3-4 minutes, or until most moisture has been released. Add black beans and mix.
Add beef, taco seasoning, tomatoes and corn to black bean and mushroom blend. Mix and cook until heated through.