Heat the oil in a large saucepan or Dutch oven over medium heat. Add the onion and cook, stirring occasionally, until soft, 5 to 7 minutes. Add the sausage and cook, crumbling it with a wooden spoon, until browned, about 8 minutes. Add the tomato paste and cook, stirring, for 2 minutes. Stir in the parsley and cilantro and cook for 1 minute more. Add the broth and chickpeas and bring to a boil. Add the frozen spinach and simmer, partially covered, for 10 minutes, stirring occasionally with a fork to separate the leaves. Stir in 1/2 teaspoon salt and 1/4 teaspoon pepper.
Divide the toasted bread, if using, among individual bowls and spoon the stew on top.