2) Brush the steak with oil and season with salt and pepper on both sides. Cook on one side until golden brown and slightly charred, about 3 to 4 minutes. Turn the steak over and cook to medium-rare, about 3 to 4 minutes longer. Allow to rest for 5 minutes then slice against the grain into 0.5cm thick slices.
3) Fill each tortilla with some lettuce, 3 to 4 pieces of meat and some onion, griddled tomato salsa, sour cream and avocado.
For the griddled tomato salsa:
1) Heat the griddle to high. Meanwhile, heat the oil in a small saute pan and saute the chillis, onion and garlic until soft.
2) Brush the tomatoes with oil and season with salt and pepper. Griddle on both sides until slightly charred and soft.
3) Transfer the tomatoes and the chilli mixture to a food processor; add the lime juice and salt and pepper and process until smooth.
4) Add the coriander and pulse a few times (there should be flecks of coriander in the salsa.) Transfer to a bowl.