Dice the onion, slice the garlic and red pepper. Slice the choi sum, keeping stems and leaves separate.
Heat olive oil in an ovenproof pan over medium heat. Add the onion with a pinch of salt and cook 5–6 minutes until soft. Add garlic and cook 1 minute, then add pepper and choi sum stems. Cook 3–4 minutes until just softened.
Stir in the gochujang, soy sauce, rice vinegar, tomato purée and maple syrup.
Pour in the coconut milk and add the butter beans. Simmer 8–10 minutes until glossy and creamy. Stir in the choi sum leaves until wilted.
Mix the panko with olive oil and sesame seeds. Scatter over the beans and grill for 5–6 minutes until golden and crisp.
