Place first 4 ingredients on a double layer of cheesecloth. Gather edges of cheesecloth together; tie securely. Combine cheesecloth bag, stock, and next 6 ingredients (stock through saffron) in a large Dutch oven; bring to a boil. Reduce heat; simmer 10 minutes. Add tomato and chicken; simmer 20 minutes.
Remove cheesecloth bag and chicken; discard cheesecloth bag. Cool chicken slightly, and chop. Add chicken, spinach, salt, pepper, and beans to broth mixture, and cook 2 minutes.
Rub cut sides of garlic halves over one side of each bread slice, and discard garlic. Place 2 bread slices in each of 6 bowls; ladle 1 2/3 cups soup over each serving.