Chimichurri, a thick herb mixture from Argentina, is a garlicky sauce that is tamed by parsley, oregano, and olive oil.
Combine all ingredients except for the steak in a container with a tight-fitting lid. Add 1/2 cup water, and shake well until mixed thoroughly. Add Tabasco to taste. Refrigerate until ready to serve; the sauce will keep up to 1 week in the refrigerator.
When ready to serve, preheat a grill, or set a grill pan coated with olive-oil cooking spray over medium-high heat until hot. Place the steak on the grill; cook until well browned, about 10 minutes. Turn, and cook until medium rare, about 10 minutes more.
Remove from heat; set steak aside for 10 minutes before cutting. Serve steak with chimichurri sauce on the side.