1) Have barbecue pre-greased and preheated to medium-high.
2) Place steak in 1 bowl and onions in another. Using a knife, make a paste by combining garlic and 1/4 tsp salt. Whisk together garlic paste, rice vinegar, soy sauce, 2 tbsp of canola oil, cumin, and ground black pepper. Divide marinade between steak and onions. Refrigerate for 1/2 hr.
3) Before grilling, allow steak and onions to come to room temperature. Place steak on griddle and cook about 4 mins per side for medium-rare. Discard marinade. When done, let steak rest before slicing.
4) Place onions face down on griddle and cook until slightly soft, about 6 mins per side. When done, cut onions into wedges.
5) Sprinkle paprika over potatoes and toss with remaining canola oil. Place on grill and cook until soft inside, about 6 mins per side. Season with salt when done.
6) In a large bowl combine steak and juices, onions, potatoes, tomatoes, coriander, and reserved marinade. Toss gently and reseason with salt and pepper if needed. Serve warm.