If you're not grilling skirt steak, you should be: It's a great cut for marinating, it cooks in minutes, and it's especially beefy, tender, and juicy—as long as you buy the right kind. For this recipe, we chose the outside skirt steak, which is 3 to 4 inches wide, and avoided the wider, far less tender inside skirt steak. To make the most of this steak's ample surface area, we submerged it in a citrusy, garlicky mojo marinade. Soy sauce in the marinade seasoned the meat, and its glutamates…