Open the bun and place on a flat surface in front of you.
Use a circle cooke cutter or a cup to get 1 slice of cheese the same size as the bun. Place the cheese and lettuce on the bun, making sure they are contained inside the bun except for a small bit of lettuce sticking out the top to resemble a fin.
Use a pairing knife or small cookie cutters to cut circles, triangles, hearts, and teardrops out of the remaining piece of cheese. Slice the blueberry in half.
Assemble the fish and place inside the lunchbox along with seaweed snacks, fruit skewers, and salt water celery.