To make the beef: Mix the crushed garlic, cumin, scallion, salt and pepper together to make a marinade for the meat.
Rub the garlic cumin marinade on the thin steaks and let marinate for a couple of hours or overnight.
Grill or fry the steaks over high heat to desired doneness. Since they are relatively thin they wonu2019t take too long to cook. Set aside.
To make the mushrooms: Heat the olive oil in a sauce pan over medium heat. Add the onions, mushrooms, garlic and thyme and season with salt and pepper. Cook for about 7 minutes or until they are golden brown, stirring often.
To assemble: top each arepa with beef and mushrooms. Garnish with fresh cilantro and serve warm.