Coat slow cooker with non-stick cooking spray. In a small cup, mix cornstarch & cold water until cornstarch is dissolved.
With the exception of the meatballs, pour all ingredients (including the cornstarch mixture) into the bottom of the slow cooker. Stir well to make sure all ingredients are incorporated.
Add meatballs to the mixture. Stir again, making sure all frozen meatballs are coated. Note: the sauce will not entirely cover the meatballs, so just spoon the sauce over the meatballs so they get one good coating.
Cook on high for one hour. Stir and serve. If you plan to serve from the slow cooker, turn the temperature down to Warm after the first hour of cooking.
Notes
No slow cooker? No problem. Pour wet ingredients into a medium saucepan and stir well. Add frozen meatballs. Cook on medium high until the sauce is thick & bubbly. Reduce heat & cover.