1. Divide the lemon slices, garlic, rosemary, and ¼ cup olive oil between two large sealable plastic bags. Add two halves of chicken to each bag, and seal well. Shake the bags to coat the chicken in the seasoning. Marinate the chickens, refrigerated, for at least 3 hours, but no more than 24 hours.
2. Preheat the oven to 450°F. Remove the chickens from the marinade, and pat dry. Season each portion with salt and pepper to taste. Heat two 12-inch ovenproof sauté pans over medium heat. Pour 2 tablespoons oil into each pan and heat the oil. Put 2 portions of chicken into each pan, skin-side down, and weigh them down with foil-wrapped bricks. Lower the flame and continue to cook until the skin becomes golden and crispy, approximately 5 minutes.
3. Put the pans of chicken, with their bricks, in the oven and cook for 15 minutes. Remove the bricks, turn the chickens over with tongs, and cook for another 5 minutes. Remove the pan from the oven, turn chickens skin-side up, and let rest for 5 minutes.
6. Place one chicken half on each of 4 plates, drizzle with Parsley Pistou, and serve.