Spray the crock pot with nonstick cooking spray. Place the frozen meatballs in the crock pot.
Make sauce: In a small bowl, whisk together honey, soy sauce, hoisin sauce, Worcestershire sauce, garlic, ketchup, sesame oil, and red pepper flakes.
Pour the sauce over the meatballs and gently stir to coat.
Cover and cook on LOW for 3–4 hours, or on HIGH for 1.5–2 hours, stirring the meatballs halfway through the cook time. Meatballs should be heated through and sauce bubbly.
Garnish with sesame seeds and green onions if desired. Serve over rice, noodles, or steamed veggies.