Sauté the garlic and onion for about 1 minute, then add the steak. Cook for around 4 minutes until the meat is nicely browned and no longer pink.
Wipe the skillet clean and place it back on medium heat. Lay a corn tortilla in the pan, sprinkle a layer of shredded cheese, then add some of the cooked steak and onion mixture.
Top with a second tortilla. Press gently with a spatula and cook for 2 minutes until the cheese starts to melt and the tortilla becomes slightly crispy.