Preheat the oven to 180C/350F.
Combine all of the salsa ingredients in a large mixing bowl. Leave at room temp and give it a good mix before serving.
Place a large cast-iron or heavy-based pan over high heat. Pat the steaks dry with kitchen/parchment paper then generously season both sides with salt and pepper. Once the pan is very hot add 1 tbsp oil, leave for 5-10 seconds, then add both steaks. For medium-rare leave undisturbed for 2 minutes, then flip and fry for a further minute. Add the butter and garlic and baste for a further minute then remove and rest the steaks to one side for 5 minutes.
As they rest, spread the tortillas out on 2 trays and sprinkle each one with cheese. Place in the oven for 3 minutes, or until the cheese melts. During this time you can roughly smash the avocado, although if you're short on time you can just scoop it out and smash onto the tacos as and when you're serving.
Very thinly slice the steaks, ensuring you slice with the knife at an angle and against the natural grain of the meat.
Stack the tortillas: smashed avo + pinch of salt, steak + some resting juices if desired, salsa, feta, hot sauce. Tuck in and enjoy!