Slice the steak into very thin pieces. I like to kind of “shave” it into pieces with a sharp knife because I find that it’s so perfectly thin and tender that way. Once sliced, place the steak in a baking dish or ziplock bag.
In a bowl, whisk together the olive oil, garlic, sugar, soy sauce and worcestershire sauce. Pour it over the steak and marinate for at least 30 minutes. (a few hours is fine too!)
Heat a cast iron or stainless steel skillet over high heat. You want the skillet HOT because we are only cooking the meat for about 1 minute. Add the vegetable oil to the skillet and once it’s shimmering, remove the steak from the marinade and add the steak (don’t crowd the pan, you will probably need to do this in batches) to the skillet. Cook for 1 minute, flip and cook for 30 seconds on the other side. Place the steak on a plate and repeat with the leftover steak.
To assemble the sandwich, spread the avocado horseradish over the baguette. Top with a few slices of butter lettuce. Add on the onions, sliced steak, radish and thai basil. Drizzle on extra horseradish. Slice and serve!