Melt butter in a large skillet over medium heat; cook and stir onion and apple slices in the melted butter until tender, about 5 minutes. Transfer onion and apple to a bowl.
Place pork chops in the same skillet; cook over medium heat until pork chops are browned on both sides, about 5 minutes per side.
Mix applesauce, brown sugar, mustard, and cinnamon into onion and apple mixture.
Place pork chops in a 9 x 9-inch baking dish; season with salt and black pepper. Spoon applesauce mixture over pork chops; cover dish.
Bake in the preheated oven until pork chops are no longer pink in the center, about 30 to 45 minutes. An instant-read thermometer inserted into the center should read at least 145 degrees F.