Warm a little oil in a frying pan over a medium heat. Add the chicken and onion and cook and stir until the chicken is no longer pink in the centre and the onion is soft. Add the curry powder and continue cooking for 2 minutes. Remove from the pan and set aside.
To the same pan add the lemon juice and stir to deglaze the pan. Add grapes and soften, mix in yoghurt and heat through. Stuff into pittas, top with cucumber and eat hot or cold.