Heat oil in heavy large saucepan over medium-high heat. Add onion and mushrooms and saute until golden brown, about 10 minutes. Add broth and bring to boil. Stir in orzo. Reduce heat to medium-low. Cover and simmer until orzo is tender and has absorbed all liquid, stirring occasionally, about 15 minutes. Remove from heat. Stir in pine nuts and parsley. Season to taste with salt and pepper and serve immediately.