Mix together soy sauce, sesame oil, sugar and garlic.
Place a bowl or plastic zip bag and add steak, turn to coat.
Marinade for 2 hours to overnight.
Remove steak for marinade and grill to medium or desired doneness.
Let rest for 5 minutes and then slice thinly against the grain.
Mix together mayo and chili garlic sauce. Refrigerate until ready to serve.
Place sliced steak on corn tortilla. Top with cabbage, radishes and green onions. Top with sauce
Notes
Slice the meat going across the grain, this makes the meat more tender. I like to cut it fairly thin, about 1/8 of an inch thick.
If you are using skirt steak, I recommended marinating for 24 hours if possible. Skirt steak is not as tender as flank steak and the extra marinating time helps make the meat more tender.
Don't overcook the beef, I prefer my meat medium. Use a meat thermometer to ensure the right temperature (135 - 145 degrees F). After it has reached your desired doneness, remove from the pan so it doesn't continue to cook.