In a bowl, mix together all your ingredients for the marinade. Add your steak to a food safe bowl or bag, then pour the marinade over top. Make sure to mix around thoroughly as to get all parts of the steak marinated. Marinate the steak for at least 4 hours in the fridge but ideally overnight.
The next day, preheat your fire for direct grilling (around 400F).
Pull out your steaks and discard the marinade. Add your steaks to the grill to cook for about 4-4.5 minutes per side or until they are 125F internal. I prefer to cook flap steak a little longer since it is such a thick & fatty cut. Char up some lemons & lemons while the steak cooks if you desire.
Once the steak is done, pull it off and let it rest for 5-7 minutes. As the steak rests, mix together the Thai Chili Sauce in a bowl.
Slice up the steak against the grain, top with the chili sauce and enjoy!