Finely chop the vegetables and mix them in a bowl with the previously flaked tuna. Add the mirin, saké, sesame oil and soy sauce to the mixture and mix everything together.
Fill the wrappers with this mixture, seal them and fry them in sunflower oil until they turn golden. Next, add a little water to the frying pan and cover it so the centre of the gyozas cook properly.
Plate the gyozas and decorate with a few tuna chunks, glazed peppers and chives.