Bring a large pot of water to the boil with a pinch of salt. Add pasta and cook for about 10 minutes or until al dente.
Meanwhile, heat butter in a large fry pan on a medium heat and cook onion, garlic and mushrooms for 4-5 minutes.
Drain pasta, reserving about ¼ cup of the water.
Remove the fry pan from the heat and add drained pasta, yogurt, reserved water, parmesan and lemon juice and toss well through the mushroom mixture. Season to taste with salt and pepper.
Serve pasta with a handful of rocket leaves and a sprinkle of parmesan.
