1: Place the flank steak in a 9×13 pan.
2: Pour lime juice over the steak and let marinate for 30 minutes at room temperature.
3: In a small bowl, combine lime zest, salt, sugar, pepper, chili powder, cumin, paprika, oregano, and cinnamon.
4: Rub both sides of the steak with the spice mixture, pressing with your fingers to help the rub adhere.
5: Preheat the grill to high heat.
6: Lightly coat a paper towel with oil and carefully rub it over the grill rack.
7: Place the steak directly on the grill and cook for 5 minutes on each side.
8: Remove from the grill and let the steak rest on a cutting board, covered with foil, for 10 minutes.
9: While the steak is resting, warm the corn tortillas on the grill or on a gas flame.
10: Cut the steak into strips against the grain.
11: Place steak strips in the corn tortillas and top with red onion, avocado, cilantro, and queso fresco.
12: Squeeze lime juice over the tacos if desired and serve warm.
