Prep ingredients: Thinly slice the chicken. Slice the onion, carrot, bell pepper, and mushrooms. Roughly chop the Chinese cabbage. Mince the garlic and ginger.
Cook curry paste: Heat oil in a pot over medium heat. Add red curry paste and stir-fry for about 30 seconds until fragrant.
Add aromatics: Add garlic and ginger and cook briefly, about 30 seconds, stirring so they don’t burn.
Add vegetables: Add onion, carrot, and bell pepper. Stir-fry until slightly softened.
Add broth: Pour in water and add the chicken bouillon cube. Season with fish sauce, sugar, and pepper. Stir until dissolved and bring to a gentle boil.
Cook chicken: Add the chicken and simmer for 3–4 minutes, until just cooked through.
Finish: Add mushrooms and Chinese cabbage. Simmer until the cabbage wilts and mushrooms are tender. Serve hot.