Heat one tablespoon of olive oil in a large pot over medium-high heat. Add half of the sliced mushrooms and saute until golden brown. Season with salt and pepper, remove and set aside
In the same pot, melt the butter and remaining tablespoon of olive oil and saute the onions and garlic until translucent
Add the remaining half of the mushrooms and cook until brown
Mix in the rice and ¼ cup of vegetable stock to deglaze the pot, scraping the bottom to release any browned bits and pieces stuck to it
Pour in the rest of the vegetable broth, and add the chopped parsley. Simmer, covered, for about 15 minutes or until the rice is tender and there is no liquid left in the bottom of the pot
Remove from the heat and stir in the reserved browned mushrooms and sliced green onions. Cover and let stan for about 10 minutes more. Serve warm