In a large 12-inch skillet, heat the oil over medium-high heat until it is simmering and hot. Season the pork chops on both sides with salt and pepper. Brown the pork chops for 1-2 minutes on each side in the hot oil until golden. Transfer the chops to the slow cooker. Add the garlic to the drippings in the skillet and stir constantly over medium heat until the garlic is aromatic and golden (but not burned or it will turn bitter!). Stir in the soy sauce, broth, brown sugar and red pepper flakes; cook and stir until sugar is dissolved. Pour over chops.
Cover the slow cooker and cook on low for 7 to 8 hours until the meat is tender. If using bone-in pork chops, fish out the bones from the slow cooker. Remove the chops from the slow cooker to a shallow pan or plate – they will most likely be falling apart in tenderness at this point. In a small bowl, combine the cornstarch and cold water until smooth. Whisk the cornstarch slurry into the sauce in the slow cooker. Return the chops to the slow cooker. Turn the slow cooker heat to high and cook for 30 minutes to an hour longer, until the sauce is slightly thickened. If you want a super duper thick sauce, once you remove the chops from the slow cooker, pour the sauce into a pan and place it over medium heat on the stove. Add the cornstarch slurry and bring the sauce to a boil. Boil for 1-2 minutes until the sauce is thick. Add the pork and heat through.
Serve the tender chops over potatoes or rice and garnish with green onions, if desired.