Whisk together soy sauce, mirin, vinegar and miso until completely combined and set aside.
Place flank steak on cutting board and cut into 2 inch slices, making sure you cut against the grain of the meat.
Place steak slices into a resealable bag and pour marinade on top of it. You may have to use two bags, dependent upon the size of your resealable bags.
Remove the air from the bag and seal, then move the steak strips around so that they get coated by the marinade.
Allow to marinate for 2 hours.
Once you have finished marinating remove steak slices from the marinade and discard what is left of the marinade.
Trim the stalks from the asparagus, then rinse and dry with paper towels.
Grab a bunch of three asparagus stems and wrap a slice of steak around them and secure with a toothpick, then place the parcel of steak and asparagus on a baking sheet.
Continue until you have created as many parcels as your steak and asparagus allows.
Drizzle with olive oil and sprinkle with kosher salt.
Place in a preheated oven at 425 and cook for approx. 45 minutes, but check on progress to make sure you do not overcook the steak.
Allow to sit for approx. 5 minutes and remove toothpick.
Sprinkle with sesame seeds before serving.