Salt and pepper the chicken pieces well on both sides. Put the chicken pieces skin side up in a casserole dish without too much extra room--a bit crowded is fine. Mix together the oil, lemon juice, and oregano, and pour all around the chicken. Scatter the lemon slices over the chicken and tuck the garlic cloves, if using, down into the oil here and there. Cook in a hot oven until it’s done, basting several times. (I have had good luck with 400° for an hour to an hour and 15 minutes, depending on the size of chicken pieces.)