Hot sesame oil (Rayu chilii oil) - or sriracha (optional)
1. For the filling. Put 1 tbsp oil in a large pan over medium-high heat. Add the drained tuna and cabbage (or chinese cabbage), red pepper. Continue stir frying until they are soft. Pat them dry on paper towel to drain extra liquid from the vegetables, then transfer them into a large bowl.
2. Add all seasoning ingredients and combine them well. Let the mixture cool completely.
3. Place a spoonful of the mixture in the center of a gyoza wrapper and wet the edge of wrapper with fingertip. Make pleats on one side, then fold over and seal to close. Continue with the rest of the gyoza wrappers until you used all filing.
3. Heat vegetable oil in a large frying pan over medium-high to high heat. Add some of the gyoza (depend on the pan size) and cook them until golden brown and crispy on the bottom. Add hot water (about 100ml), cover pan with the lid and let it steam over medium heat for about 5 mins or until the water evaporates. Repeat with remaining gyoza.