This one is the goods. I marinate my fajita beef steaks before grilling them whole over charcoal and then I slice them after they achieve medium rare doneness. This marinade provides the Tex-Mex flavor that you're seeking when making fajitas. I use both sirloin steaks (cut 2 thick) and flatiron steak for fajitas - both are really tender and the marinade makes them even moreso. If you don't have rice vinegar, just use either plain white vinegar or white wine vinegar. This recipe will generate enough marinade for 4-5 pounds of meat. I hope you enjoy the flavor as much as we do!