Heat the olive oil in a Dutch oven over medium-high heat. Add the sausage, breaking it into crumbles with a wooden spoon. Cook until no longer pink, about 8 minutes.
Add the diced onion, sliced carrots, and thinly sliced celery to the pot. Sauté until the onions are translucent and the vegetables are soft, about 5-6 minutes.
Add the minced garlic and Italian seasoning, cooking for an additional minute until fragrant.
Stir in the undrained white beans, fire-roasted diced tomatoes, and chicken stock. Season with cracked black pepper and optional red pepper flakes. Place the thyme sprig on top.
Bring to a boil, then reduce heat to medium-low. Simmer uncovered for 10-15 minutes to blend the flavors. Taste and adjust seasoning with salt and pepper as necessary before serving.
Serve the soup in bowls, garnished with chopped parsley. Enjoy immediately. Leftovers can be stored in the fridge for up to a week or frozen for up to 3 months.
Notes
For a spicier kick, add more red pepper flakes. Adjust salt according to your taste preference.