1. Heat the oil in a frying pan and saute the chicken pieces on both sides. Transfer to a heavy casserole. In the oil remaining in the frying pan, adding a little more if necessary, sauté the onion and garlic until the onion is tender but not browned. Transfer to the casserole with the pineapple, oregano, red pepper, salt and pepper to taste.
2. Add the pineapple juice and stock to the casserole, cover and simmer for 20 minutes. Add the lentils and cook for 25 minutes longer.