Heat the oil in a pan and gently cook the potatoes, scallions, garlic, ginger, parsnips and carrots together till they are softening but not coloured. Add the curry paste and stir for a moment to mix through.  Pour over the coconut milk, then fill the can half full with water and stir into the curry.  Bring to bubbling and simmer gently till all the veggies are tender. Add a squeeze of citrus juice and stir in the spinach or chard at the last minute. Cook till wilted. Season with freshly ground black pepper.
Serve with plain white rice or noodles – chopsticks optional!