Make the marinade by combining all the marinade ingredients in a large plastic bag.

Add the steak, seal the bag, then place it in the fridge to marinate for two hours.

Remove the steak from the fridge for 15 minutes before cooking.

Make the avocado dressing by combining the avocado, cilantro, sour cream, and lime juice in a food processor. Add enough water to make a pourable dressing, then taste for seasoning and add salt and pepper as needed.

Take the steak out of the bag and discard the marinade. Cook the steak to your liking on a hot grill or grill pan, then let rest for 10 minutes. 

Place some salad leaves and shredded cheese into a serving bowl.

Slice the steak and place it on top, then drizzle with a little of the dressing. Serve the rest of the dressing on the side.