Line large rimmed baking sheet with plastic wrap. Gently mix all ingredients in large bowl. Using moistened hands and scant 2 tablespoonfuls for each, roll meat mixture into 1 1/2-inch meatballs. Arrange meatballs on sheet. Heat oil in heavy large ovenproof pot over medium heat. Add onions; saute about 15 minutes. Add garlic, cinnamon, turmeric, and saffron; stir 2 minutes. Add broth, tomatoes with juice, and raisins. Preheat oven to 350°F. Bring stew to simmer. Stir in carrots. Carefully add meatballs to stew; gently press into liquid to submerge. Sprinkle 1/4 cup cilantro over. Cover pot; place in oven. Bake until meatballs are cooked through and carrots are tender, about 35 minutes. Sprinkle spinach over stew. Cover and bake until spinach wilts, about 5 minutes longer. Gently stir to mix in spinach, being careful not to break meatballs. Remove cinnamon sticks. Season tagine with salt and pepper. Spoon couscous into bowls; top with tagine. Garnish with cilantro and lemons. Available in the Asian foods section of some supermarkets and at Asian markets.