Dice the potatoes, onions, and carrots.
Heat cooking oil in a pan and sauté the prepared vegetables.
When the vegetables are about half cooked, add the tuna and stir-fry together.
Season with soy sauce, sugar, minced garlic, and pepper.
Add water and simmer until most of the liquid is absorbed.
Once the vegetables and tuna are fully cooked, turn off the heat and serve.