In a mixing bowl, whisk the oil, 2 teaspoons of the mustard, lime juice and jalapeno, until well blended. Season both sides of the flank steak with the sea salt and pepper. Place the steak in a large resealable plastic bag and pour the marinade over the steak. Seal the bag completely and shake several times, to evenly distribute the marinade. Place in the refrigerator and marinate overnight.
Remove the steak from the refrigerator and bring to room temperature. Set aside. Preheat the fryer. Preheat the grill.
Place the steak on the grill and cook for 3 to 4 minutes on each side for medium rare. Remove from the grill and allow to rest for a couple of minutes before slicing.
In the cup of a blender, combine the roasted pepper, egg, lemon juice, remaining 2 tablespoons of mustard, and garlic. Blend on until smooth. Season with salt and pepper. With the blender running, slowly drizzle in the oil until the mixture is slightly thick. Add the buttermilk and continue to blend for 1 minute. Season with salt and pepper. Cover and refrigerate for at least 1 hour. The dressing will keep for up to 2 days in the refrigerator.
Fry the tortilla chips in batches until golden brown. Remove and drain on paper towels. Season with salt. Set aside.
In a large mixing bowl, toss the lettuce with as much dressing as you wish. Season with salt and pepper. Toss well. Cover the bottom of a large rectangle plastic container with a lid with the lettuce. Slice the steak on a bias into 2 inch slices and place over the lettuce. Layer the onions, tomatoes, corn and cheese over the steak. Cover with the lid and refrigerate until ready to use. The salad can be made one day ahead of time.
When ready to serve, remove the peel and pit of the avocado. Small dice the avocado and season with salt and pepper. Add to the salad along with the tortilla chips. Toss well and serve.
