Put the oil in a large pot over medium heat. When it's hot, add the mushrooms, onion, and black pepper. Cook and stir for 8 to 10 minutes or until mushrooms are browned; do not drain. Stir in garlic, chili powder, cumin, and oregano and cook for 1 minute more.
Add the beans and tomatoes. Bring to boiling; reduce heat and cook, covered, stirring occasionally, until the tomatoes have begun to break down and the flavors have melded, about 15 minutes. Serve over chips or rice, if desired, and garnish with cilantro and cheese.