Make the sauce: Whisk all sauce ingredients in a small saucepan. Bring to a boil, then reduce heat and simmer for about 2-3 minutes, until thick enough to coat the back of a spoon. Set aside.
Make the meatballs: Preheat the oven to 350 degrees F. In a large bowl, mix all ingredients except for the oil with your hands. Roll the mixture into balls roughly 1” in diameter. Place them on a baking sheet coated with nonstick cooking spray, brush the tops with the oil, and bake them for 12 minutes or until cooked through.
Serve the meatballs with sauce and additional chopped basil and green onion, if desired.