Mix together the cold water and the cornstarch in a medium saucepan – stirring to remove any lumps.
Add remaining ingredients, except meatballs, to the saucepan and stir to combine.
Cook over medium heat, stirring constantly, until mixture begins to thicken. Remove from heat.
Add frozen meatballs to slow cooker and pour the thickened sweet and spicy sauce over the meatballs.
Cook on low for 3-4 hours or on high for 1-2 hours or until meatballs are heated through. Garnish with sliced green onion (opt.) and serve over rice. *Note: You may want to stir these half way through if you are cooking on high.