Meanwhile, melt the butter in a frying-pan and gently sauté the onion and bacon until they are soft and golden. Add the garlic and cook for two minutes, then add the peas, cream and lemon zest.
Season and bring to the boil, then turn down the heat, add the parsley and some seasoning and allow everything to meld for a minute or so.
Drain the pasta and return it to the pan in which it was cooked, adding the sauce. Season, toss everything together and check the seasoning (I sometimes add a squeeze of lemon instead of more salt).
Pour into a heated serving dish and serve with some parmesan thrown over the top. Offer more parmesan on the side.