Add the rest of the ingredients (except for the parmesan and swiss cheese) to the crockpot and add onions. Turn crockpot on high for 4 hours, or on low for 8 hours, or overnight.
When ready to serve, sprinkle parmesan cheese in the soup, and ladle soup into an oven (or microwave safe) bowl, and add a piece of swiss cheese on top. Place in oven preheated to low broil and place soup in oven to melt the cheese. Leave in oven for 1-3 minutes, or until cheese is lightly golden brown. Alternatively, you could microwave the soup for 1-3 minutes, or until the cheese is melty! Enjoy!