Meanwhile, in 10-inch skillet, heat oil over medium heat. Add onion; cook 2 to 3 minutes or until tender. Stir in chipotle chili and the adobo sauce, meatballs and 2 tablespoons water. Cover; reduce heat to low. Cook 3 to 4 minutes, stirring occasionally or until thoroughly heated. Remove meatballs from skillet. Spoon 1/2 teaspoon of the sauce into each cup. Top each with one meatball half, cut side up.