If the meatballs are frozen, no need to thaw. Just adjust the cooking time for the meatballs to cook through.
In a pan, heat oil. Saute minced garlic for 30-40 seconds until the raw smell is no more.
Add the rest of the ingredients to the pan except cornflour. Whisk everything and bring to a low boil.
Make a cornstarch slurry by mixing cornstarch with 2 tablespoons of water. Lower the heat and slowly stir in the slurry into the pan.
Let the sauce simmer for 30 seconds. Add the meatballs(if using fresh cooked meatballs). Toss for another 2-3 minutes for the sauce to thicken and coat meatballs.
If using frozen meatballs, then after adding to the pan, lower the heat and cover for 10-12 minutes for the meatballs to thaw and cook through. Note- Cooking time may vary depending on the size of the meatballs.