For the ribs: Cut each rack of ribs in half. Sprinkle the ribs with salt. Scatter the garlic and ginger in the bottom of a 6-quart slow cooker, then top with the ribs, bone-side down. Cover and cook on low heat for 8 hours, making sure not to lift the lid or otherwise disturb the ribs.
Transfer the ribs to a baking sheet and loosely cover to keep warm.
Strain the cooking juices from the slow cooker into a large skillet. Stir in the honey, soy sauce and vinegar. Bring to a boil over medium-high heat. Stir together the cornstarch with 2 tablespoons water in a small bowl, then whisk into the skillet and simmer until thickened, about 1 minute.
Cut the ribs into pieces and put back in the skillet with the sauce. Toss to coat. Turn off the heat and keep warm.
For the slaw: Whisk together the mayonnaise, vinegar and honey in a large bowl. Add the coleslaw mix, cilantro and red onion and toss to coat well. Season with salt and pepper if needed. Tip into a serving bowl.
Serve the ribs in the skillet with the slaw alongside.
To reheat the ribs, bake in a 9-by-13-inch pan at 350 degrees F for 20 minutes.