In a small bowl, combine dark soy sauce, oyster sauce, hoisin sauce, and mirin. Whisk together until well blended.

Heat oil in a large skillet over high heat. Add sliced onion and minced garlic, sautéing for about 1.5 minutes until golden.

Add bite-sized chicken thighs, stirring frequently. Cook for about 2 minutes until cooked through.

Pour prepared sauce into the skillet, cooking for an additional minute while stirring. Add carrot and red capsicum, sauté for 1 minute.

Make a space in the skillet and pour in water. Bring to a simmer, then add ramen noodles and cook according to package instructions.

Use tongs to toss the noodles with chicken and vegetables. Add cabbage and cook until wilted.

Remove from heat, serve in bowls, and garnish with sliced green onion if desired.