In a large pot, heat a tablespoon of oil over medium heat.
Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for 1 minute more.
Add the ground beef and cook until browned, breaking it apart as it cooks.
Season with salt, pepper, and thyme, mixing well.
Add the diced carrots, celery, and bell pepper and cook for another 5 minutes.
Stir in the cubed potatoes and cook for a minute.
Pour in the beef broth and bring the mixture to a boil.
Add the can of diced tomatoes and reduce heat to a simmer.
Cover and let it cook for about 20-25 minutes, or until the vegetables are tender.
Adjust seasoning if necessary, then serve hot.