Remove the steak from the fridge and let it come to room temperature, cover with baking paper and bash it with a rolling pin to tenderise and make it all roughly the same thickness.

Place the buns into a hot oven to warm through and toast a little on the outside.

Season the steak all over with salt and pepper.  Place a large, heavy bottomed pan on high heat, once really hot, drizzle the steak with olive oil, then put into the pan and cook for 3 minutes on each side for medium, or to your liking.  Remove to a plate and rest 1 minute, then slice into strips against the grain.

Cut the buns in half, spread with mayonnaise, then layer avocado, lettuce, steak and tomato relish.  Top with the other piece of bun, press down lightly and serve!