- In a medium saucepan over medium heat, combine brown sugar, soy sauce, garlic powder, ground ginger, honey, and rice vinegar. 
- Bring to a gentle boil while stirring occasionally. 
- In a small bowl, mix the cornstarch with water until smooth, then stir it into the sauce. 
- Continue to cook and stir until the sauce thickens—this takes about 1–2 minutes. 
- Place the frozen meatballs in a large slow cooker. 
- Pour the sauce over the meatballs and stir to coat evenly. 
- Cover and cook on low for 4 hours or until heated through. 
- Garnish with sesame seeds and green onions before serving, if desired.