Heat the oil in a large frying pan over a medium heat. Add the shallots and stir-fry for 4–5 minutes. Add the mustard seeds, curry leaves, chilli, ginger, turmeric, cumin and peppercorns, and stir-fry for a further 1–2 minutes until fragrant.
Add the carrots, courgette, beans and potato to the pan. Pour in the coconut milk and stock and bring to the boil. Reduce the heat to low, cover and simmer gently for 12–15 minutes until the vegetables are tender. Season to taste, remove from the heat and squeeze over the lemon juice just before serving.