Preheat the roasting oven. In a small baking bowl, combine the melted butter, oil, and crushed chile peppers, and in a second baking bowl, combine the chopped onion, parsley, and garlic. Add 4 tsp of the butter and oil mixture to the parsley and onion mixture, stir to form a paste, and set aside. Quickly rinse the chicken quarters under running water until cooled and wipe with paper towels. Pat dry, then brush both sides with the remaining butter-and-oil mixture and season lightly with salt. Grill the quarters, skin side down, on the broiler rack of the grill pan 10 cm from the heat source. After 5 min, baste the chicken with the remaining butter-and-oil mixture and grill for another 5 min. Repeatedly baste the chicken and place skin side up on the broiler. Grill for another 10 to 15 min, basting the chicken every 5 min with the juices that are in the broiler pan. The juices should come out clear when you poke a chicken thigh with the tip of a sharp knife.
Using a metal spatula, spread the onion and parsley paste on each quarter (pressing firmly until smooth) and grill for another 3 to 4 minutes, or until the coating is lightly browned. Place on top of a preheated serving bowl and pour the gravy over the top. Garnish with lemon quarters.