Open and drain the can of tuna, then transfer it to a medium-sized bowl.
Dice the celery and juice half of the lemon, or until you have about 1 tablespoon of juice.
Wash the cucumber thoroughly, then use a peeler to create thin slices of cucumber for rolling.
Cut off the top one-fourth of the avocado and remove the pit from the larger portion. Set the smaller piece aside for garnishing, then dice the larger part of the avocado.
Add the diced avocado, mayonnaise, lemon juice, celery, chili powder, salt, and pepper to the bowl with the tuna. Mix until everything is well combined.
Take about 1 ½ tablespoons of the tuna mixture and place it on a slice of cucumber. Roll the cucumber slice around the mixture and place the roll on a plate, seam side down. Continue this process until all the cucumber rolls are plated.
Slice the remaining portion of avocado into thin slices. Dice one or two slices and garnish the top of the cucumber rolls. Arrange the avocado slices on the plate.
Finish with a sprinkle of paprika for color, and enjoy!