A roast is good. I tried slicing the beef first, then marinating, but it overwhelmed and was too tangy. Thus I take a half pound or so of roast (chuck, round, whatever - just some leaner meat) and marinate awhile in lime juice and oregano. Flip it at some time. Slice into tasty bite bits and basically stir fry til browned. Serve on corn tortillas that have been warmed. Best way I've found is to have some spray oil, lightly spray them and cook briefly on each side til floppy and warmed. Garnish with salsa cruda, guacamole (I'm having some tonight!!) and sour cream (or mock sour cream if, like us, you eschew dairy products). Makes for some yummy-ness, though tends to induce carnivore naps around our house.