Prepare the sushi rice according to package directions.
Preheat oven to 400F and line a sheet pan with parchment paper. Add your cubed sweet potatoes to the sheet pan and roast for 20 minutes, until the cubes are fork tender.
Cut the nori sheets into quarters. Now, spread a heaping spoon of rice on each quarter one at a time, until one side is covered in a thin layer of rice. Then transfer to a muffin tray and set one in each well, squishing it down so it makes a "cup".
Drizzle the teriyaki sauce onto the cooked sweet potato and toss. Then, transfer the sauced up sweet potato to each nori cup, about two tablespoons in each. Transfer the muffin tin to the oven for around 10 minutes, until everything is slightly crispy.
Remove the muffin tray from the oven and top your cups with vegan spicy mayo, green onions and sesame seeds, as desired.