1. Prepare the sushi rice according to the package instructions. In a small bowl, stir together the rice vinegar, sugar, and salt. Pour the mixture over the rice and stir to coat it. Let it cool and refrigerate overnight.Assemble the pumpkin sushi:
2. To make each piece, place a 2 1/4-inch circle of smoked salmon in the center of a square of plastic wrap.
3. With clean hands, mold 1 3/4 tbsp. of prepared rice into a round shape. Set it on top of the salmon.
4. Gather the plastic wrap and twist it tightly, compressing the filling into a neat ball. Unwrap it and set the ball, salmon side up, on a platter. Cut features from nori and set them in place (tweezers are handy for this).Assemble the monster sushi:
5. Repeat the above steps, but substitute a thin slice of avocado for the salmon and form the rice into an oblong shape instead of a round one (twist the wrap gently to shape the avocado without squishing it).