Add all marinade ingredients to a blender and purée until smooth.
Place short ribs into a bowl or zip top plastic bag and pour the marinade over. Cover or seal the top and refrigerate for a minimum of 4 hours, or overnight (12 hours tops).
Heat gas, charcoal or pellet grill to 350°F. (See Note 1 for other cooking options)
Shake excess marinade from short ribs and place on grill grates. Grill on first side for 4 minutes, then flip ribs over and cook for an additional 4 minutes. The edges will caramelize and become crispy.
Allow the meat to rest for 5 minutes, then cut thin slices across the grain. Garnish with sliced green onions and serve over steamed rice.
Notes
Other cooking options - No matter which cooking method you use, the cook time for flanken ribs is the same; 3-4 minutes per side.
On a gas, charcoal or pellet grill, cook the ribs at 350°F
For a smoker, set the temperature to 400°F
An oven broiler only has one setting
Stovetop - Use high heat and a cast iron grill pan or skillet. Allow pan to get searing hot before adding the ribs