Heat the oil in a saucepan over medium heat. Add the onion and garlic and cook, stirring occasionally, for 5 minutes or until the onion softens. Add the tomato and stock or water and bring to the boil.
Add the cannellini beans, lamb and green beans and cook for 2-3 minutes or until heated through. Add the spinach and cook for 1 minute or until just wilted. Season with salt and pepper. Ladle soup among serving bowls and serve.
