Melt 1/2 the butter in a skillet over medium heat. Stir in the onions & garlic, and cook until golden brown. Mix in orzo, mushrooms, and remaining butter. Cook and stir 5 minutes, until butter is melted and mushrooms are tender.
Pour water and wine into the skillet, and bring to a boil. Reduce heat to low. Season with salt, and pepper. Cook 7 to 10 minutes, until orzo is al dente. Stir in the Parmesan cheese and parsley to serve.