Stir lemon juice, olive oil, salt, curry, cayenne pepper and garlic together in a small bowl.
Place chicken in slow cooker.
Pour olive oil mixture over the top, stirring to coat the chicken.
Cook on high for 5-6 hours or low for 7-8 hours.
Stir cucumber and yogurt together.
Serve chicken in pita bread, topped with yogurt sauce and tomatoes.