Heat 2 tbsp oil in a skillet, add chopped garlic and sauté until golden.
Add sliced chicken and cook until no longer pink.
Toss in onions, cabbage, carrots, and capsicum; stir-fry for 5–6 minutes.
Add soy sauce, vinegar, salt, sugar, and black pepper; cook until well combined and moisture evaporates.
Let the mixture cool. Mix flour with a little water in a small bowl to make a sealing paste.
Place a spoonful of filling on each spring roll sheet, roll tightly, and seal the edge with the paste.
Deep fry rolls in hot oil until golden and crisp.
Drain on paper towels and serve hot with Katsu Sauce or your favorite dip.