In a medium bowl, combine 2 cups orange marmalade, 2 cups BBQ sauce, 1 cup sweet chili sauce, the zest of one orange, and 1 tablespoon white vinegar; stir until the mixture is smooth and uniform.

Spray the slow cooker insert with cooking oil.

Add the 32-ounce bag frozen fully cooked meatballs (about 40–50) to the slow cooker.

Pour the sauce over the meatballs and gently stir or toss to coat the meatballs evenly.

Cover and cook on HIGH for 2 to 3 hours, gently stirring once about halfway through the cooking time.

When heated through, stir once more, transfer to a serving dish, and garnish with diced green onion before serving.