As the meat cooks, the orange, garlic and beef juices caramelize, creating a sweet, meaty flavor.
In a blender, combine orange juice, olive oil, garlic cloves, oregano, cumin, salt, orange zest and pepper; blend until smooth. Pour marinade over flank steak and let sit, uncovered, at room temperature while you light or preheat grill. Or you can cover and refrigerate steak for several hours or overnight.
When ready to cook, brush off any excess marinade solids from steak and grill over high heat, turning once, until done to taste, about 3 minutes a side for rare. Slice in thin slices across the grain to serve.