Pick over the chickpeas, cover with cold water, and soak overnight at room temperature. Drain chickpeas and rinse well with cold running water. Drain and set aside.
Heat the olive oil in a medium stockpot or Dutch oven over medium-high heat. Season the chicken pieces with 1/4 teaspoon each of salt and pepper. Add the chicken in batches, and cook until well browned, about 4 minutes per batch. Remove the chicken from the pot and set aside. Add the onions and celery and cook until softened, about 4 minutes. Add the ginger, turmeric, pepper, cinnamon, and nutmeg and cook, stirring constantly, for 1 minute. Return the chicken to the pan and add the tomatoes and their juices, stirring well. Stir in the chicken stock, lentils, and chickpeas and bring to a boil. Reduce heat to medium-low, cover, and cook at a gentle simmer for 1 hour.
Add the rice and the remaining 1/2 teaspoon of salt and return the soup to a simmer. Cook covered for 30 minutes. Remove the lid, add the cilantro, parsley, and lemon juice and cook, uncovered for 5 minutes.
Ladle into warmed soup bowls and garnish with fresh cilantro sprigs.