Pulse all marinade ingredients in blender until a rough paste, scraping down blender jar as needed.
Combine marinade and meat in gallon-size zipper-lock bag; press out as much air as possible and seal bag. Refrigerate 1 hour, flipping bag after 30 minutes to ensure that meat marinates evenly.
Drain and discard marinade. Grill steak, over medium high heat for 7-9 minutes on each side or until meat reaches desired doneness. Let rest for 10 minutes before slicing.
Transfer steaks to cutting board; tent loosely with foil and let rest 5 minutes. Slice steak very thinly on the bias. Split Loaf, brush a bit of oil on the inside, and grill for about 1 minute until warm and slightly toasted. Mix together the Kikkoman Sriracha Sauce and mayonnaise, and smear onto the toasted bread. Compose your sandwich with sliced steak, arugula, and brie.
Created by Chef Jet Tila and inspired by Kikkoman.