Slice off both ends of the cucumber, and using a metal straw (or very stiff plastic one), pierce through the center of one end of the cucumber and push the straw through to the opposite side, removing the seeds as you push.
A chopstick or small paring knife works well for this job, too. Continue to pierce through the original hole, cleaning out the cuke center, until the opening is ¾-inch wide. To make cleaning easier, you can cut the cucumber in half so you have two tubes instead of one.
Hold the cucumber vertically on a flat surface, and using the straw or a chopstick if needed, stuff half of the empty space with rice and avocado, then stuff the cucumber with any vegetables you are using.
There is no wrong way here. Just try to pack in as much rice and as many vegetables into the cuke tube as possible. Slice the stuffed cucumber horizontally into 6 to 8 rounds (like a sushi roll).
Sprinkle the bites with salt and sesame seeds. Serve immediately with the Ranchy Dressing for dipping.