Cook tagliatelle in lightly salted boiling water until al dente; drain and transfer to a heated serving bowl.
Heat a dry frying pan over medium heat; add bacon and cook until the fat renders. Increase the heat and cook until bacon is crispy; transfer bacon onto kitchen paper, leaving the fat in the pan. Add garlic, parsley and walnuts to pan and cook over medium heat for 1 minute; season with salt and pepper.
Add the bacon and tagliatelle to the pan; toss everything together and serve with grated Parmesan cheese.