Place the sliced potatoes in a pot and cover with water. Bring the pot to a boil over high heat, then let simmer until the potatoes are tender, about 5 minutes. Drain the potatoes and set aside.

Heat oil in a large skillet over medium high heat. Add in the garlic and sauté for about one minute, then add in the potatoes. Continue to sauté, stirring every few minutes, until they are mostly golden brown, about 8-10 minutes.

Add in the green beans, mushrooms, and butter, and continue to sauté until the green beans are slightly softened, about 5 minutes. Season the with oregano, salt and pepper.