In a bowl, mix together the flour, garam masala and turmeric.
Whisk in 200ml cold water and the lemon zest until smooth, then chill for 30 minutes.
Half-fill a heavy-based saucepan with oil and heat until a drop of the batter sizzles when it hits the oil.
Quickly stir the chillies, potato, onion, drumsticks, spring onions and coriander into the batter and season.
Working in batches, spoon the mix into the oil. Fry for 2-3 minutes, or until crisp and golden. Remove with a slotted spoon, drain on kitchen paper and keep warm while you cook the remaining pakoras. Scatter with coriander and serve with raita and chutney, if you like.