Preheat oven to 375 degrees. Spray a 13 x 9 inch baking dish with non-stick spray.
Season each pork chop with salt and pepper.
In a small bowl, combine brown sugar, ketchup, Dijon mustard, and garlic; whisk well.
Place pork chops in a prepared baking dish and spoon the brown sugar mixture over them.
Add onion slices to the top of each pork chop.
Cover with aluminum foil and bake at 375 degrees for 30 - 45 minutes.
Baste pork chops halfway through cooking and uncover. Continue to bake until the pork chops are cooked through.