In a bowl, whisk together honey, soy sauce, apple cider vinegar, olive oil, minced garlic, oregano, thyme, black pepper, and red pepper flakes (if using).
Place the pork tenderloin in the slow cooker.
Pour the honey garlic mixture over the pork, ensuring it's well coated.
Cover and cook on LOW for 6-7 hours or on HIGH for 3-4 hours, until the pork is tender and cooked through.
Once done, carefully remove the pork from the slow cooker and set aside.
In a small bowl, mix cornstarch and water to create a slurry.
Pour the cooking liquid from the slow cooker into a saucepan over medium heat.
Whisk in the cornstarch slurry and simmer for 2-3 minutes until the sauce thickens.
Slice the pork tenderloin and serve with the thickened sauce drizzled over top.
Garnish with fresh parsley if desired.