Ideally, you’ll want two baking sheets here. Arrange the tomatoes and garlic in a single layer across one. And then arrange the onion across the other. Sprinkle the salt across both and drizzle with the olive oil. Toss well, and place in the oven to roast for 35-45 minutes, or until the onions are golden, and the tomatoes have released their liquids and concentrated a bit. Remove from the oven.
Transfer the tomatoes and garlic to a soup pot, and use a hand blender to pulse a few times. You don’t want the tomatoes completely smooth, go for a slightly rustic texture. You’re done with the hand blender, so you can put it away. Stir in the onions and four cups of water. Bring to a simmer over medium high heat and stir in the cayenne and saffron. Taste, and season with more salt at this point to your liking. Stir in the bread and chickpeas and bring back to a simmer for 10 minutes or so, gently stirring now and then along the way.