Devein the prawns then rinse and pat dry with kitchen paper. Rub the turmeric and chilli powder on the prawns and set aside.
Heat the oil in a pan over a high heat, add the prawns and stir fry until they just turn opaque then remove using a slotted spoon. Set aside.
Add the onions to the pan and fry over a medium heat until the edges start to brown. Add the garlic and ginger pastes and the chopped chillies and fry until the oil separates from the onion mixture.
Add the spinach and salt and cook until the water released from the spinach has evaporated.
Return the prawns to the pan with the spinach mixture and cook for a couple more minutes. Taste and adjust the seasoning adding more salt if needed.
Serve immediately garnished with the sliced red chilli.