In a large skillet over medium heat, add the first 5 ingredients (beef through cumin) and sauté for 10 minutes, until the beef is cooked through and vegetables are tender.
Spoon the beef mixture into the mushrooms, season with salt and pepper to taste and place on a large baking sheet. Place in oven and cook for 10 minutes, until mushrooms are tender. Top with cilantro and serve warm.