Slice cucumber and avocado into thin long strips/sticks.
Season cook sushi rice with sushi vinegar, mix well.
Lay a piece of plastic wrap on a flat surface or on top of bamboo mat. If you're using non-stick mat, skip this step.
Tear a sheet of nori down to ¾ of its size.
Spread half the rice evenly onto Nori.
Flip the nori upside-down.
Arrange cucumber and avocado slice on top of the nori.
Lift, tuck and roll into uramaki-style sushi roll.
Uncover the wrap, arrange marinade tomato slices on top of sushi roll.
Recover w/ plastic wrap and bamboo mat, lightly apply pressure to shape.
Slice and serve with desired vegan sauce.