Rinse a 1- to 2-cup bowl with cold water and lightly pack 1/4 of the sushi rice salad into it. Invert onto a plate. Repeat to shape remaining portions.
Cut nori sheets into quarters. Moisten sliced avocado with rice vinegar.
Sprinkle sushi rice salads equally with shaved bonito. Alongside each, arrange 1/4 of the nori, avocado, salmon, pickled ginger, and radish sprouts. Sprinkle servings with tobiko caviar.
To eat as sushi, put some of each ingredient on a piece of nori and add chili mayonnaise to taste; fold nori over filling. Or eat as a salad with a knife and fork, adding chili mayonnaise to taste.
Nutritional analysis per serving without mayonnaise.