Combine the sauce ingredients in measure cup. Pour about 1/3 of mixture over the flank steak and let sit about 15-30 minutes. Reserve the rest.
Put barley and water in pot over medium-high heat. Bring to a boil. The barley may start to foam when it starts to boil. Cover the pot and turn down so the barley simmers. Start checking the barley after 25 minutes, then every 5 minutes after that until done. The barley should be soft, but still a bit al dente.
Meanwhile, sauté the bell pepper and onion on medium low heat, until soft and beginning to get colour, about 10 minutes.
When the barley is done, cover with the lid and let sit until ready to serve.
Heat heavy bottomed cast iron pan over medium heat. Add 2 tbsp canola oil. Place flank steak in pan and fry until golden brown (about 5 minutes). Turn to the other side and cook about 10 minutes more. Cook until the internal temperature is about 145F. Let rest for 10 minutes before slicing.
Serve barley in the bowl first – then add sautéed and fresh veggies as you like. Slice meat and dress with leftover sauce, to taste.