Cook rice according to package directions.

In a small bowl, combine the vinegar, sugar, and salt. Pour into rice and stir to combine. Lay a piece of seaweed on a sushi mat (cover the mat with plastic wrap for an easier clean-up), shiny side down. Using a large wooden spoon, place a scoop of rice on the seaweed and spread evenly, leaving 2 inches uncovered at the top or bottom. Cut cucumber, avocado, and imitation crab into thin strips. Line up fillings across the center. Roll up sushi. Slice in half. To prepare the tempura batter, combine the flour, water, and egg in a shallow bowl. Dip each roll in the batter, then dip in the breadcrumbs. Fry until breadcrumbs are golden brown, about 2 minutes per side. When ready to serve, slice each sushi roll into small pieces with a sharp serrated knife. Serve with dipping sauces: Sweet Dipping Sauce or Spicy Mayonnaise Dipping Sauce