Thaw the frozen udon noodles in the microwave. Shred the cabbage, cut the carrot into matchsticks, and thinly slice the onion.

Heat a frying pan and add the tuna with its oil. Break up the tuna, then add the carrot, onion, and cabbage in that order. Stir-fry until the vegetables are tender.

Add the udon noodles to the pan. Season with the ingredients marked A, then adjust the flavor with salt and pepper to taste. Finish by drizzling with sesame oil.