In a medium-size bowl, combine all the above ingredients; whisking to blend.
Place flank steak in a 9-x 12-inch dish or a large zip-lock plastic bag; cover with the prepared marinade. Cover, refrigerate, and let marinate overnight or at least 8 to 10 hours, turning several times.
When ready to cook, remove from refrigerator 30 minutes prior to grilling. Prepare and preheat your grill for cooking. Grill the marinated steak 5 to 7 minutes per side, is medium rare or until the internal temperature reaches desired temperature on your meat thermometer (see below). NOTE: This steak is best cooked rare to medium rare. If overcooked, the meat can by dry and chewy.
Rare - 120F
Medium Rare - 125F
Medium - 130F
Remove from heat and let steak rest 5 minutes before slicing. With a sharp knife, slice steak thinly against (diagonal) the grain.
Southwest Marinated Flank Steak Recipe: https://whatscookingamerica.net/karencalanchini/marinatedflanksteak.htm