Preheat the grill. Using a fork or mini whisk, mix the miso, sriracha, and sesame oil ….& pinch salt and pepper together in a small bowl to make a paste. Brush liberally onto both sides of the portobello mushrooms.
Using veggie peeler or mandolin, cut the cucumber into long thin ribbons. (You can always just slice them into very thin disks) Place them in a medium bowl along with scallions and add the dressing ingredients and gently toss.
Make the carrot slaw the same way. Place in a small bowl, toss with dressing ingredients. To save time you can combine both the carrots and cucumber (and double the dressing) and serve them together in one bowl – but I prefer them separate, just for “prettiness”, but it’s not essential. 🙂
Make the Asian Guacamole, by placing everything in a small bowl, mashing and stirring a bit until creamy and combined. It doesn’t have to be smooth. Sprinkle with sesame and chili flakes.
Grill the portobellos, top sides down first, for 4-5 minutes over medium heat, until juicy and tender. Flip, grill a few more minutes. Grill the Buns.
Assemble the burgers….spread buns with generous amount of Asian Guac, place the portobello- gills side up ( to catch all the flavorful juices) then mound with cucumber ribbon and carrot salad, a little squeeze of sriracha, optional pickled ginger. Use the remaining Asian Guac on the bun tops, and top the burgers.