In a large non stick frying pan, sauté onion, carrots, and mushrooms for about 5 minutes. You can add some water to the pan. This way you can avoid using any type of fat. Add in the garlic and sauté for a minute.
In a large crockpot, add the ingredients from the skillet with the remaining ingredients. Cook on high for 2-3 hours, or until vegetables are tender.
Notes
This soup freezes well. To thaw, place in the fridge for 24 hours and then reheat.