Lightly coat bottom of large nonstick skillet with cooking spray and heat pan until hot. Add onion and garlic and cook, stirring often, until soft, about 5 minutes. Add bread cubes and cook, stirring occassionally, until golden brown. Remove from heat.
Pour broth into large pot and heat over medium heat. Put half the bread mixture and 1/2 cup tomatoes into food processor or blender and process until coarsely ground. Scrape mixture into pot with broth and repeat with remaining bread and an additional 1/2 cup tomatoes.
Add remaining tomatoes, chickpeas, spinach, saffron, salt and pepper to pot. Cook, stirring occasionally, until heated through, about 10 minutes. Serve warm.