Gently fry the onion in the oil in a heavy bottom pan over a low to medium heat for 5 minutes until translucent and browning at the edges. Add the garlic, red peppers, ginger and chilli and fry for a further 2 minutes.
Add the massaman paste, stir well and cook for 1 minute.
Add the fish sauce, stir to combine and cook for 1 minute.
Add the strips of meat, stir well to coat the meat and fry gently until the meat softens and absorbs some colour.
Add the water chesnuts and bamboo shoots and cook for a further 2 minutes until heated through.
Add the coconut milk, mix well, cover and simmer gently for 15 minutes.
Remove the lid and raise the heat to reduce the liquid until a creamy consistency.
Squeeze over the juice of a lime and serve.
For the Side:
While the curry is simmering, top and tail the spring onions, then slice diagonally into 5cm lengths.
In a heavy bottom frying pan, heat the rapeseed oil over a medium heat. Add the spring onions and fry for 2 minutes turning frequently. Sprinkle over a pinch of salt and a drizzle of the toasted sesame oil and turn over a couple of times. Cook for a further 2 minutes.
Put a spoonful of the onions on top of the curry to serve with some basil leaves.
Notes
For a milder curry, deseed the chilli before slicing.For a lighter curry use light coconut milk.