Mix all soup ingredients in slow cooker.
Mix meatball ingredients together in large bowl, then roll into 22 to 24 meatballs and carefully place down into soup.
Cooking times: LOW – 5 hours, add mushrooms, cook 1 more hour. HIGH – 2-1/2 hours, add mushrooms, cook 30 more minutes. If making soup on the stove, simmer on low for 2-3 hours, add mushrooms and cook until tender.