To CookAdd sauce ingredients into a bowl and mix together until fully combined. Heat over medium-low heat, stirring to avoid burning. Take off heat when sauce is reduced by half. Set aside to cool.Add sushi seasoning to cooked brown rice, mix and sit for 15 mins. Add vegetables into a large mixing bowl. Add in ½ cup flour and salt, and toss until coated thoroughly.In a separate bowl, prepare the tempura batter by incorporating the remaining plain flour, potato starch and ice water. Then add the batter with vegetable mix, tossing to combine.Heat the vegetable oil in a wok. Spooning bits of the vegetable batter into the oil, using a chopstick to shape it into a round form.Remove from oil when golden and place on wire rack or drain on paper towel. To shape sushi buns, spoon 2-3 tbsp of sushi rice into an egg ring and press to mold into shape. Place sushi buns on heated pan to sear the surface. Assemble the burger by adding wasabi, pickled ginger, cucumber and desired amount of sauce before topping off black sesame seeds on top of sushi bun.