In a medium bowl, mix together the lime juice, orange juice, cumin, garlic, olive oil, salt and pepper.
Place the steak in the bowl and coat thoroughly with the marinade. Reserve for one hour at room temperature (see note), or refrigerate for up to 8 hours.
In the meantime, preheat the grill medium heat or 400°F (204°C) and prepare toppings, i.e. dice the tomatoes, dice the red onion and crumble the cheese.
Spray the grill grates with oil spray.
Place the steak on the grill and cook for 3-4 minutes per side until medium-rare or medium, using an instant-read thermometer to check doneness (130-140°F or 54-60°C).
Remove steak to a cutting board, cover with foil and let rest for 5 minutes to preserve juiciness.
Cut the steak crosswise against the grain into thin 3-inch (8 cm) slices, about ¼ inch or ½ cm. Reserve.
Please a skillet over medium-high heat. Add a tortilla and heat for 30 seconds until puffy. Remove to a plate for assembly into a steak taco. Repeat for remaining tortillas.
Add a few slices of steak to the middle of the tortilla, followed by toppings, cheese and cilantro. Repeat for remaining tortillas. Serve and enjoy!