Season the short ribs with lemon pepper and garlic salt. Heat the oil in a large skillet over medium-high heat. Working in batches, brown all sides of the short ribs. When browned, place in slow cooker on top of sliced onions.
In a mixing bowl, combine the remaining ingredients. Pour over the top of short ribs. Cover and cook on high setting for 3 to 4 hours or low for 8 to 9 hours.
Cook's Note: Five-spice powder is a blend of ground spices used extensively in Chinese cooking. It usually consists of cloves, cinnamon, fennel seed, star anise, and Szechuan peppercorns. It can be found in the spice section of the grocery store.