In a Dutch oven or ovenproof pot over medium heat, brown the onion in the oil for 10 minutes. Add the Parmesan rind, thyme, beans and broth. Mix well. Bring to a boil. Skim as needed. Add the garlic, spices and lemon zest. Season lightly with salt and pepper. Cover and bake in the oven for 1 hour or until the beans are tender and the broth has thickened slightly.