Wash the potato and poke it all over with a fork. Place on a plate and cook in the microwave on high for 10 minutes, or until tender. Let cool slightly.
Once the potato is cool enough to touch, slice in half and scoop out the potato from the skin and place in a bowl with the milk and butter. Using a potato masher or fork, mash the potato until no longer clumpy and the milk and butter are distributed. Set aside.
In a large soup pot or dutch oven, heat olive oil over medium-high heat.
Add the beef, onion, carrots, and bell pepper. Stir and cook until the meat is almost browned.
Add the minced garlic and continue to cook until the meat is completely browned.
Pour in the beef broth, oregano, salt, and black pepper. Whisk in the tomato paste and mashed potato.
Bring to a boil and then cover and lower the heat to a simmer. Let simmer for 30 minutes.
Serve hot.