Using fork, pierce steak at 1/2-inch intervals. In large bowl, whisk vinegar, sugar, sambal oelek and salt. Reserve 1/4 cup mixture for later use. Add soy sauce, oil, chili powder and cumin to remaining vinegar mixture. Add steak; turn to coat. Let stand 10 minutes to marinate.
To make pickled onions: In medium microwaveable bowl, combine water and reserved vinegar mixture. Microwave 2-3 minutes, or until hot. Add onions, submerging in vinegar mixture. Let stand at room temperature until cool.
Preheat grill to high heat. Grill steaks 1-2 minutes on each side, or until medium rare. Let stand 5 minutes before slicing against grain into thin strips.
Serve with tortillas, salsa, pickled onions, cilantro, avocado and radishes.
