Bring a large pot of salted water to a boil and cook the tagliatelle until al dente according to package directions.
Season the chicken breast with half of the sea salt and black pepper.
Heat olive oil in a large skillet over medium-high heat and sear the chicken until golden and cooked through, then set aside to rest.
In the same skillet, sauté the finely minced shallot, garlic, and sliced mushrooms until the mushrooms are browned and tender.
Slice the rested chicken into thin strips.
Drain the pasta, reserving a small splash of the starchy pasta water, and add the pasta to the skillet with the mushrooms.
Stir in the sliced chicken, truffle oil, and reserved pasta water, tossing quickly until everything is coated in a glossy sauce.
Garnish with grated parmesan, fresh parsley, and the remaining salt and pepper before serving immediately.