Prepare the rice according to directions on package. Once cooked, set rice aside in a mixing bowl and season with salt and rice wine vinegar to taste. Allow rice to cool for 20 minutes.
In a bowl, mix together the flour, cornstarch, and baking powder. Season with salt. Slowly whisk in the water until a thick batter forms.
Place a toothpick or bamboo skewer into the shrimp so that it stays straight. (Leave a portion of the toothpick sticking out so its easy to remove.)
Heat the oil in a saucepan or skillet over medium heat until you start to see a little white smoke coming from the oil. Dip the shrimp into the batter to coat well and carefully place it in the oil. Fry until golden brown (you can check the shrimp with a thermometer to an internal temperature of 120°F). Once done, set aside on paper towels to drain excess grease. **Very important** Once they are cool enough to handle, gently remove the toothpick.
Dampen your hands with water, portion and spread the rice on the nori sheets. Spread to all corners, covering evenly. (Leave 1/2" along one edge of nori sheet uncovered, as this will be how you seal your roll.) Carefully flip the sheet over onto a bamboo sushi mat or parchment paper so that the rice side faces down and the nori side faces up.
Layer down the middle: avocado, crab meat, tempura shrimp. Starting at the side of the nori that is covered with rice to the edge, begin to roll the sushi gently pressing firmly to make sure the roll remains tight. Repeat the tightening process with sushi mat. You can do this a few times if necessary. Set aside to dry before slicing.
Mix the mayo, sriracha, garlic powder, salt and pepper in a bowl.
Slice the sushi roll into 6-8 pieces (you may have to rinse or wipe the blade in between slices to prevent sticking and tearing).
Drizzle with spicy mayo, teriyaki sauce and sesame seeds. Garnish with some tempura crunchies if desired (see pro tips below).