Saute the onions and garlic in a large soup pot (I use a little oil; I'm sure you can use Pam, water or stock if you're concerned about fat).
Add the remainder of the ingredients, bring up to a boil and then turn the heat lower and simmer for about an hour, stirring occasionally. I just cook until it tastes right. Generally I'll cook it covered for 30-40 minutes and then leave the cover off until its done. I don't know if that makes a difference though.
I'm sure you can add carrots, celery or other veggies to this but I like it with just onions and garlic. I take it to work for lunch.