In a large skillet, over medium high heat, melt the butter. Season the chicken on both sides with salt and pepper. Cook for 3 minutes on each side, then transfer to a plate and keep warm.
Return the skillet to the heat, and add the onion,sauteing for about 4 minutes. Add the cinammon, paprika and curry powder. Saute for about 30 seconds more, then add the apples, tossing well to coat the apples with the seasoning. Cover the pan, reduce heat to low, and simmer for 5 minutes or until apples are tender but not mushy.
Uncover the pan and stir in the vinegar. In a small glass, mix the water and cornstarch, adding it to the pan. Stir and bring to a simmer. Return the chicken to the skillet, cover with the sauce, cover the skillet and cook for 6-8 minutes or until the sauce has thickened and the chicken is fully cooked.