To Make on Stove-Top: Add onions to a small microwave-safe bowl. Cook for 1 minute, to soften.
In a large pot, heat olive oil. Add garlic, softened onions, and sauté for a minute or so. Stir in chicken broth, diced tomatoes, beans, Italian seasoning, and a little salt and pepper, to taste. Bring it to a simmer. Continue to simmer for 10 minutes.
In the meantime, cook tortellini separately. Follow package directions. Drain and set aside.
To the pot of soup add cooked chicken, cooked tortellini, spinach, and milk. Let simmer for 5 minutes until heated completely. When ready to serve, sprinkle each serving with 1 teaspoon of Parmesan cheese, if desired.
To Make in Crock-Pot: Add all ingredients except the chicken, tortellini, spinach, and milk, into a crock-pot and let it cook on low heat for 3 ½ hours. Next, mix into soup the cooked chicken, spinach, and milk. Cook for another 30 minutes until heated through. In the meantime, cook tortellini separately. Once the soup is ready, stir in cooked tortellini. When ready to serve, sprinkle each serving with 1 teaspoon of Parmesan cheese, if desired.