Heat the oil in a pan, sauté the onion. Add the rice, cook while stirring until translucent. Gradually add the stock, stirring frequently, so that the rice is always covered with liquid, simmer for approx. 10 mins. until the rice is al dente.
Spread the risotto onto the tortillas, leaving a border of approx. 3 cm on one side. Drizzle soy sauce over the rice, allow to cool. Spread over the tuna, tomatoes and salad, roll the tortillas up tightly.
Cut in half diagonally to serve.