Mix canned tuna, mayonnaise, and finely chopped green onion in a bowl to make tuna mayo.

Make a vertical cut in each chikuwa and stuff them with the tuna mayo mixture.

In a bowl, beat the egg and mix in grated cheese.

Coat the stuffed chikuwa with the egg mixture.

Heat salad oil in a frying pan over medium heat and place the coated chikuwa in the pan.

Gradually pour the remaining egg mixture over the chikuwa while cooking, turning them until the egg is fully cooked.