Heat the oil in a Dutch oven or soup pot over medium heat and cook the onions about 15 minutes, stirring periodically, until they are slightly browned and definitely golden. Mmmmm. Prep the other vegetables.
Add the carrots and celery, salt and pepper a bit and stir, then let cook over medium heat until softened a bit, 3-4 minutes. I don't time it, just stir and watch. Add the zucchini and stir, then cook another few minutes. Stir in the cabbage, tomato paste and chicken broth. Add the Parmesan rinds if you have them. (They do add a good taste but once I over did it with the rinds so now I'm of the more is less mindset. I added a piece about 1" long.)
Stir well and bring to a boil, then reduce the heat and simmer, covered, stirring now and then, for half an hour or so.