This hearty, stew-like meatball soup is loaded with warm, flavorful spices like cinnamon, cumin and allspice, making it the perfect meal for a cold autumn day. Delicious as is, try serving it with a dollop of Greek yogurt, some torn fresh herbs, and/or some warmed pita bread.
Grate 1/2 onion over a medium bowl, collecting any juices in the bowl. Add the beef, 2 teaspoons cinnamon, the cumin, allspice, and 3/4 teaspoon each salt and pepper; mix well. Form into 24 meatballs (about 1 rounded tablespoon each).
Heat 2 tablespoons olive oil in a large Dutch oven or other heavy pot over medium-high heat. Add the meatballs and cook, turning occasionally, until browned, about 6 minutes. Remove the meatballs to a plate. Wipe out the pot with a paper towel.
Dice the remaining 1/2 onion. Cut one of the lemon halves into 4 wedges and juice the other half. Heat the remaining 1 tablespoon olive oil in the pot over medium-high heat. Add the onion and carrots and cook, stirring, until they begin to soften, about 4 minutes. Season with salt and pepper. Add the remaining 2 teaspoons cinnamon and cook, stirring to coat, 1 minute.
Add the tomatoes, chicken broth, rice and meatballs to the pot. Bring to a boil, then reduce the heat to a simmer and cook until the meatballs are cooked through and the soup thickens, 8 to 10 minutes. Remove from the heat and stir in the lemon juice; season with salt and pepper.
Divide the soup among bowls. Serve with the lemon wedges.