Preheat oven to 450ºF. In a small bowl, whisk together mustard, honey and salt. Season pork chops with salt and pepper on both sides and arrange in a baking dish. Spoon honey-mustard mixture evenly over both sides of chops, then top with onions. Bake for 10 minutes, flip chops, then bake for about 10 minutes more, or until pork reaches 145ºF with thermometer inserted in thickest part. Allow chops to rest for 5 minutes before serving.