Place the pork shoulder roast in the slow cooker.
In a medium bowl, whisk together the honey, soy sauce, apple cider vinegar, minced garlic, grated ginger, black pepper, salt, and red pepper flakes if using.
Pour the honey garlic mixture over the pork roast, ensuring it is well-coated.
Cover the slow cooker and cook on low for 6-8 hours or until the pork is tender and easily pulls apart with a fork.
Once cooked, remove the pork from the slow cooker and place it on a serving platter.
Pour the cooking liquid into a saucepan and bring it to a simmer over medium heat.
In a small bowl, mix the cornstarch with water to create a slurry, then add it to the simmering sauce.
Stir the sauce until it thickens, about 2-3 minutes.
Drizzle the thickened sauce over the pork roast and garnish with chopped green onions before serving.
