Combine steak, onion and capsicum in a shallow baking dish. Whisk together garlic, lime juice, oil, vinegar, cumin, salt, pepper and chilli in a small bowl. Pour over steak mixture; toss to coat. Refrigerate, covered, for 1 to 2 hours.
Preheat grill. Cook steak about 10 cm from heat, 2 minutes each side. Add the onion and capsicum. Spoon any remaining marinade over steak and vegetables. Grill, turning meat and vegetables occasionally, until the meat is cooked as liked and vegetables are crisp-tender, about a further 7 minutes. Leave meat to stand 5 minutes.
Cut meat diagonally across grain into thin slices. Divide meat, onion and capsicum evenly between warmed tortillas. Top with cheese. Place under grill just until the cheese melts, about 30 seconds. Fold tortillas over filling and serve.
on the menu
Other flatbreads such as lavash and pita bread can be used for this recipe. Warm them lightly in the oven, under the grill or in the microwave. You can vary the cut of beef used depending on your taste and budget.