In a bowl, combine juices, oil, garlic, cumin, chili powder, and salt and pepper to taste.
Steak should be marinated in the mixture for 30 minutes up to 2 hours in the refrigerator.
Set your grill to high heat and apply oil to the grates
For medium-rare steak, grill it for 4-6 minutes on each side. For more done, grill it longer.
Take a 5-minute break. When you return, make sure to slice thinly across the grain.
On the grill, heat tortillas and add steak, onions, and cilantro. Pour lime juice on top of the tacos.