1. Preheat a 4-quart slow cooker. Heat 2 tablespoons oil in a large skillet over high. Add onion, garlic, and red-pepper flakes and cook until softened, about 5 minutes. Add kale and cook until just wilted, 5 minutes. Transfer to slow cooker.

2. Add 1 tablespoon oil to skillet, then add zucchini and cook over high until lightly browned, 3 to 4 minutes. Transfer zucchini to slow cooker along with tomato, beans, and boiling water; season with salt and pepper. Cover and cook on high until beans are tender, 3 hours (or on low 6 hours).

3. Heat remaining 3 tablespoons oil in a large skillet. Add bread and cook over medium, turning once or twice, until golden and crisp, 5 to 6 minutes. Let cool slightly, then tear into pieces; stir into stew in slow cooker. Cover and cook on high until thick, 1 hour more (or on low 2 hours more). Season with salt and pepper; serve, topped with grated cheese and drizzled with oil.