In a large pot, heat one tablespoon of olive oil over high heat and saute half of the sliced mushrooms until brown. Season with salt and pepper, and set aside.
Add the remaining tablespoon of olive oil and the butter to the same pot. Over medium heat, melt the butter and saute the onion and garlic for about 2 minutes.
Mix in the remaining half of the sliced mushrooms and cook until brown.
Our in ¼ cup of vegetable stock to deglaze the pot. Mix in the rice.
Add the remaining vegetable stock, parsley, salt, and pepper to taste. Bring to a boil, reduce the heat, and simmer (covered) until the rice is cooked through and no liquid is left in the pot, about 15 mins.
Turn off the heat and mix in the reserved mushrooms and sliced green onions. Cover and let stand for 10 minutes so the mushrooms warm up. Serve warm.