Heat the oven to 425°F and line a rimmed sheet pan with parchment.
Rub the chicken with olive oil, salt and black pepper and roast for 16 to 20 minutes, until 165°F at the thickest point.
Stir the squeezed spinach, chopped artichokes, cream cheese and garlic powder until evenly combined.
Rest the chicken for 5 minutes, place each cutlet on a sourdough slice and spread one-fourth of the spinach-artichoke mixture over it.
Top each open sandwich with provolone and broil 6 inches from the heat for 1 to 2 minutes, until the cheese bubbles and browns in spots.
Rest the melts for 2 minutes before serving so the topping stays on the bread.