Bring a large pot of salted water to a boil and cook the tagliatelle until al dente.
While the pasta cooks, heat the olive oil in a large skillet over medium-high heat.
Season the sliced chicken breast with sea salt and black pepper, then sear in the skillet until golden and cooked through.
Remove the chicken from the pan and set aside, then add the sliced mushrooms to the same skillet.
Sauté the mushrooms until they are browned and tender, then stir in the minced garlic for 30 seconds.
Drain the pasta, reserving two tablespoons of the cooking water, and add the pasta and chicken back into the skillet.
Drizzle with the truffle oil and toss everything together, adding the reserved pasta water to create a light sauce.
Serve the pasta immediately, garnished with grated parmesan and fresh parsley.