In a large skillet, heat a small amount of olive oil. Add the quartered mushrooms and cook for 3–5 minutes until browned and softened.
Stir in the sliced onion and sauté for another 2–3 minutes until the onion starts to soften.
Add the green beans, diced tomato, minced garlic, oregano, salt, black pepper, and beef broth. Stir to combine.
Bring the mixture to a boil, then reduce the heat slightly. Let it simmer uncovered for 10–15 minutes, depending on how tender you prefer your green beans.