Place the chicken breasts in the bottom of the slow cooker.
In a medium bowl, whisk together the honey, soy sauce, minced garlic, hoisin sauce, and rice vinegar until well combined. Pour the mixture evenly over the meat.
Cover and cook on LOW for 4 to 5 hours, or HIGH for 2 to 3 hours, until the meat is tender and easily shreds with a fork.
Remove the meat from the slow cooker and transfer to a cutting board. Shred it using two forks.
In a small bowl, whisk the cornstarch and cold water to create a slurry. Stir the slurry into the liquid remaining in the slow cooker. Turn the heat to HIGH and let it bubble for 10 minutes to thicken into a glaze.
Return the shredded meat to the slow cooker, toss to coat evenly in the thickened sauce, and garnish with sliced green onions before serving.