Line a rimmed baking sheet with foil and spray with cooking spray.
Heat oil in a skillet over medium-high heat. Saute the onion and garlic for about 3 minutes.
In a large bowl combine egg, milk, breadcrumbs, 1/3 cup parsley, chili powder, and cinnamon. Mix well. Add half of the onion mixture and the beef, season to taste with salt and cayenne, and mix well again.
Form the mixture into 2-inch meatballs and place on prepared baking sheet. Spray the tops of the meatballs with cooking spray. Broil 6 inches from heat, turning to brown on all sides.
Add tomato sauce and cumin to the remaining onion and garlic mixture in the skillet. Bring to a boil over medium-high heat, stirring occasionally.
Put the browned meatballs into the sauce. Return to a boil, then reduce heat to low, cover, and simmer for about 15 minutes. Turn the meatballs occasionally with a slotted spoon while simmering.
Top with remaining parsley. Serve meatballs and sauce over couscous or rice.