Food Network teaches how to crush, slice and mince garlic. Peel off some of the papery skin from the garlic and then smash the head of garlic with the heel of your hand to loosen the cloves; if you only need a few cloves, leave the head intact and pull some off. Separate the cloves. To peel a clove, cut away the root end with your knife. Lay the flat side of the knife over the clove while holding the knife handle, then with the heel of your free hand carefully whack the knife against the garlic to separate the skin from the clove. To crush the peeled garlic, lay the flat side of the knife over the clove and smash it again. To slice peeled garlic, lay the clove flat on the cutting board and hold it with the fingertips of one hand, keeping them curled under. Using a rocking motion with the knife, make thin slices by moving the knife slowly across the clove. To mince peeled garlic, lay the flat side of a knife over the clove and smash it. Roughly chop the clove then move your free hand flat across the tip of the knife and use a rocking motion to chop the garlic until it’s finely minced.
In a 9 by 13-inch glass baking dish, combine the butter, tequila, thyme, serrano, garlic and cilantro and mix well. Transfer steak to the marinade and sprinkle with salt and freshly ground black pepper. Let stand at room temperature for 30 minutes or in the refrigerator for up to 2 hours.
Preheat a large griddle or skillet over medium-high heat and brush with olive oil. Cook the steak, turning occasionally, 6 to 8 minutes per side for medium-rare. Let rest on a plate covered with aluminum foil for 10 minutes. Cut the meat against the grain into 1/2-inch pieces.
On the same griddle used to cook the steak, over medium-high heat, place 3 (1/4 cup) mounds of cheese spaced 2 inches apart. Let cook for 3 minutes (the cheese will spread flat like a tortilla, make sure they don't stick together). After the cheese browns on the bottom (the cheese will stay white on the top side), add 1/4 cup sliced meat over half of the cheese and fold the other half over like a half moon-shaped quesadilla. Transfer to a baking sheet and cover with aluminum foil to keep warm. Repeat the procedure with the remaining ingredients.
Serve each cheese taco with sliced avocado and salsa or hot sauce.