In a large pot, heat olive oil over medium-high heat. Add the beef stew meat and brown on all sides, about 5-7 minutes. Remove the beef and set aside.
In the same pot, add the diced onion and garlic. Sauté for 2-3 minutes until the onion is translucent.
Add the carrots, celery, and bell pepper to the pot. Cook for another 5 minutes, stirring occasionally.
Return the browned beef to the pot. Add the diced tomatoes, beef broth, green beans, thyme, oregano, salt, and pepper. Bring to a boil.
Reduce the heat to low, cover, and simmer for 1.5 to 2 hours, or until the beef is tender.
If using, stir in the baby spinach during the last 5 minutes of cooking. Adjust seasoning if necessary.
Serve hot, garnished with fresh parsley.