Slice your tuna into¼-unch thick, 3-inch long, and 1-inch wide slices.
Take 3 tablespoons of cooked rice with your hands, start shaping them into an oval with a straight bottom and rounded top. Make sure the rice is not completely squeezed, and there is still room for air.
On the middle of the tuna slice, spread pea-sized wasabi piece, then place the oval-shaped rice on top. Squeeze with your index finger gently to allow them to stick together.
Flip the sushi made so that the tuna slice facing the top. Serve the sushi pieces with soy sauce, wasabi, and pickled ginger.