Pre-heat the grill or the broiler. Whisk together the soy sauce, rice vinegar, sesame oil, ginger, garlic and hot sauce in a 13 x 9 inch glass baking dish. Season the sauce with salt and pepper. Add the steak and let it marinate at room temperature for up to 30 minutes, turning a few times. Remove the flank steak from the marinade. Grill or broil on both sides for 5-6 minutes or until desired doneness. Allow the steak to rest for 5-10 minutes before slicing it. Slice the meat thinly across the grain and serve.