Preheat the oven to 350° F. Spray a 10- x 17- x 1-inch baking sheet with cooking spray.

In a large bowl, mix the turkey, egg, bread crumbs, onion, garlic, salt, pepper, grape juice and mustard until blended.

Moisten your hands and shape the turkey mixture into 1-inch balls. (It is important to make them all the same size so that they cook evenly.)

Place the meatballs on the prepared pan so that they do not touch.

Bake the meatballs 15-18 minutes or until cooked through.

In a large skillet, combine the grape juice, ketchup, mustard and onion. Bring to a simmer. Add the cooked meatballs and stir gently until the meatballs are coated with the sauce. Simmer 5 minutes. Serve warm.