Place the beef in a bowl, add with curry powder, sugar, cilantro, scallions, garlic, chiles, cumin, salt, and pepper, and mix well. Form into 4 (8-ounce) patties. Place patties on grill and grill to desired doneness. Place scallion pieces and shiitake caps on the grill and brush with the teriyaki sauce and grill until well charred.
Serve burgers on sesame buns topped with grilled scallion and shiitakes and more teriyaki sauce, if desired.