Slice each chicken breast into six diagonal strips and slice the mushrooms. Set aside. Halve the chillies lengthways and de-seed then cut into very thin long strips. Peel and finely chop the garlic and ginger. Cut all the basil from the pot and discard stalks; set leaves aside.
Heat the oil in a large non-stick frying pan or wok and stir-fry the chicken for 2 minutes, then add the chillies, garlic, ginger and stir for another minute.
Add the mushrooms and curry paste and stir for half a minute. Pour in the chicken stock and lime juice and stir for a further minute until sizzling an the chicken is cooked through.
Stir in most of the basil leaves – immediately remove from the heat and serve straight away garnished with the remaining basil leaves.