1. To prepare the steaks place the salad onions, chillies, garlic, three quarters of the fresh coriander and the ground coriander in a food processor, and blitz until you have a coarse paste. Place the steaks in a large freezer bag and add the paste. Seal the bag, releasing as much air as possible, and press the paste into the steaks until completely coated. Set aside in the fridge to marinate for at least 2 hours or preferably overnight.
2. For the relish, place all the ingredients in a small saucepan and bring to the boil over a high heat. Simmer for 5 minutes or until thickened. Pour into a small food processor and process until smooth. Set aside to cool.
3. Preheat a griddle or frying pan over a high heat. When very hot, shake off the excess marinade from the steaks and cook them for 4-5 minutes each side for medium rare, or until cooked to your liking. Set aside on a board to rest for 5 minutes, then slice thinly.
4. Meanwhile, place the jalapeno relish, little gem lettuce leaves, soured cream and diced avocado in 4 separate serving bowls. Arrange the tortillas on a platter and keep warm. To assemble, spread a tortilla with relish, top with a few lettuce leaves, some slices of beef, a teaspoon of soured cream, some chopped avocado, a squeeze of lime and a few stems of the remaining coriander. Roll up to eat.