Tortellini Soup

1 medium onion, chopped
1 garlic clove, minced
2 cup (14 1/2 ounce) low-sodium chicken broth
8 ounces cheese tortellini
1 (14 1/2 ounce) can no-salt added, Italian stewed tomatoes
1 (10 ounce) package frozen chopped spinach, thawed and drained

In a large saucepan coated with nonstick cooking spray, saut