Score flank steak on the diagonal, criss cross, both sides, with a sharp knife
Press 2 cloves of garlic into the scores on each side
Add fresh ground pepper to both sides
Juice the lemon onto both sides
Cover with wrap and refrigerate for at least 30 minutes.
Remove from refrigerator for at least 10 minutes before cooking. Preheat grill on high, or cast iron skillet if cooking inside. (Cast iron requires a bit of olive oil in the pan).
Cook on each side for at least 5 minutes before turning. It's delicious when there is a slight char to the meat.
Cook to desired temperature. Medium-rare is preferred with a slight pinkness to the meat.
Remove from heat and let rest for 5 minutes before slicing.
Cut the meat thinly on a slight angle. I find it's easy to slice the meat vertically (down the center) into 2 long pieces, especially if the steak is fairly wide. This way you can wrap any unused portions that aren't sliced, which prevents the meat from drying out when reheating it.
Serve on a salad, standalone with side, in tortilla... however you want!