Add the sliced chillies, stirring all the while, for 3 minutes, then stir in the grated ginger, finely chopped garlic, and cook, still stirring, for another 2 minutes. Spoon in the mustard and salt, stirring well to combine, then add the spinach leaves and let them wilt in the pan for 2-3 minutes, stirring regularly, then squeeze in the lime juice.