Heat a Dutch oven over medium-high. Add the bacon to the pan and cook 4 minutes or until crisp.
Remove bacon from pan with a slotted spoon, reserving 1 tablespoon drippings.
Add the onion, carrot, and celery to drippings in pan and sauté 3 minutes. Stir in the thyme, mushrooms, and garlic. Sauté 5 minutes.
Add stock and bring to a boil. Reduce heat, and simmer 8 minutes or until vegetables are tender. Add the spinach, salt, ground mustard and pepper cooking for 3 minutes. Stir in the chicken and rice.
Combine half-and-half and cornstarch in bowl, whisking until smooth. Stir into the soup and cook 2 minutes or until thickened. Top with bacon.
Notes
Soup can be made up to 24 hours in advance and stored in the refrigerator in an airtight container.