First make the guacamole. Put the avocados, tomatoes, garlic, cumin, spring onions and most of the coriander in a food processor and pulse to a chunky paste. Scoop into a bowl, season with salt, pepper and lime juice to taste, then stir in a little extra virgin olive oil.
Heat a griddle pan over a high heat. Grill the mushrooms (if using) until seared all over. Remove them from the pan and keep warm.
Season the steaks well with salt, pepper and the oregano and paprika, then bash them with the bottom of a saucepan or a rolling pin to flatten them out slightly. Rub with a little olive oil and cook in the preheated griddle pan for 5 minutes, turning them every minute, or until cooked to your liking.
Leave the steaks to rest on a plate while you make up the wraps. Lay the tortillas out on a clean work surface and spread with a little guacamole. Slice the steaks into thin strips, divide them between the tortillas and scatter with the grilled mushrooms. Drizzle with a little more oil and the resting juices, then wrap.
Top with a dollop of yoghurt, the remaining coriander leaves and some red chillies (if using). Serve with the lime wedges on the side and tuck in!