Bring a large pan of water to the boil and cook the spaghetti following pack instructions. Meanwhile, heat the oil in a large non-stick frying pan and cook the bacon for 3-4 mins until just starting to crisp. Stir in the onion and cook for another 3-4 mins, then add the mushrooms, garlic and smoked paprika, and cook for 3-4 mins more.
Pour in the chopped tomatoes, bring to the boil and bubble for about 5 mins until thickened, stirring every so often to stop it catching on the bottom. Drain the pasta and toss with the sauce. Serve with Parmesan, if you like.