Cook spaghetti in a large saucepan of salted boiling water, according to packet directions, until al dente.
Meanwhile, heat a large frying pan over high heat. Add pancetta and cook, stirring often, for 4-5 minutes until pancetta is crisp. Remove to a plate and set aside.
Add 2 tbs oil to the frying pan and heat over medium heat, add onion and garlic and cook 4 minutes until soft. Add the mushrooms, increase heat to high and cook, stirring often, for 4 minutes or until mushrooms are tender and golden. Set pan aside.
Drain spaghetti and return to the hot saucepan. Add pancetta, mushrooms and remaining oil. Toss gently over low heat for 2 minutes or until heated through. Remove from the heat, add the parsley and half the parmesan, season with salt and pepper. Toss well to combine.
Spoon into serving bowls, top with remaining parmesan and serve immediately.