Rinse chicken and pat dry. Cut each piece into 2 thin slices as follows: place chicken on a cutting board, bone-side down. Holding firmly in place under the palm of your hand, slice horizontally (as if butter flying, but cutting all the way through).
Coat chicken lightly with flour on all sides; shake off excess.
Preheat a 5-qt. sauté pan over medium heat until rim of pan is hot to the touch. Add 2 Tbsp. oil and wait about 1 more minute.
Add as many pieces of chicken to pan as will fit without crowding. Cook until lightly browned on bottom, 3 - 5 minutes. Turn and continue to cook until meat in thickest part is no longer pink (cut to test), about 3 - 5 more minutes.
As chicken pieces are cooked, place on a warm platter and keep in a 200°F/95°C oven. Add up to 1 Tbsp. more oil to pan as needed to cook the remaining pieces.
When all chicken has been cooked, add wine and lemon juice to cooking pan.
Increase heat to high and bring mixture to a boil, stirring to loosen drippings from pan. Cook, stirring often, until liquid is reduced by about half, about 3 - 5 minutes.
Stir in orange zest and marmalade. Season to taste with salt and pepper.
Pour sauce over chicken. Sprinkle with parsley and garnish with orange slices.