Begin by marinating the steak: In a bowl, mix together all the marinade ingredients. Add the steak and cover the bowl. Refrigerate while you prepare the rest of the ingredients.
Next, make the Pickled Vegetables: In a bowl mix together the sugar and vinegar, and then add the rest of the ingredients.
Next, make the mushrooms: In a large skillet, heat two tablespoons of oil on medium heat. Cook the mushrooms with the salt and pepper for ten minutes or until they're golden brown.
Next, cook the steak: In a cast iron skillet heat two tablespoons of the oil on high heat, and cook the steak in five batches until it's cooked to rare or medium rare. Add more oil, as needed.
Fill each lettuce leaf with some steak, some mushrooms and some pickled veggies. Garnish the cups with the cilantro, Fresnos, and sesame seeds. And, serve with lime wedges.