Meatballs and rice make this hearty, home-cooked soup substantial enough to serve on its own.
Mix together beef, rice, mint, cilantro, cinnamon, egg, 2 teaspoons salt, and 1/4 teaspoon pepper in a large bowl. Form tablespoons of mixture into meatballs (about 40).
Heat oil in a large pot over medium-high. Add onion and cook, stirring occasionally, until soft, about 3 minutes. Add broth, 2 cups water, tomato sauce, zucchini, and meatballs. Simmer over medium, partially covered, until meatballs are cooked through, about 25 minutes. Season with salt and pepper. Stir in spinach and serve, topped with cilantro leaves.