Drain the oil from the canned tuna and place it in a bowl. Add diced carrot, finely chopped onion, 1 egg, a pinch of salt, a dash of pepper, and 2/3 cup of flour. Mix the ingredients into a dough.

Once mixed, knead the dough with dry hands until it forms a cohesive texture.

Heat a pan with oil over low heat. Cook the patties slowly, flipping occasionally, and cover with a lid to ensure they cook through evenly.

Prepare the sauce by mixing 6 tbsp tonkatsu sauce, 3 tbsp ketchup, 1 tbsp oyster sauce, 1 tbsp corn syrup, and 2/3 cup water. Heat the mixture over low heat until it simmers for about 3 minutes.