In a large bowl, toss the chicken pieces with the olive oil. Season with salt and pepper and toss again. Heat two large (at least 12-inch) non-stick or well-seasoned cast iron pans over medium heat. Add the chicken pieces, skin side down and cover the skillets. Cook the chicken, turning it once, until golden brown on both sides, 5 to 7 minutes. Move the chicken pieces to one side of the skillet. Add the potato halves cut side down to the clear side of the skillet and cook on medium heat 15 minutes, turning them and the chicken pieces often, until evenly browned. (At this point, both the chicken and potatoes should be crisp and brown). Meanwhile, peel the onions and cut them in quarters through the core, leaving the core intact to hold the quarters together while they cook. Reduce the heat to medium-low, divide the onions, rosemary, olives and peperoncino between the skillets and cook, covered, until the onions have softened and the flavors have blended, about 15 minutes. Stir the contents of the skillets gently several times as they cook. Drain the oil from the pan before serving chicken and potatoes, sprinkle with chopped parsley and serve. Note: Cut each spring chicken into four pieces: 2 breasts/wings and two legs. You can substitute two large (about 1 ¾ pounds each) Cornish for the spring chickens. Cut the hens into 8 pieces each: 2 wings. 2 breasts, 2 thighs, and 2 legs. Cooking time will be approximately the same.