Bring a large pot of salted water to a boil and cook the tagliatelle according to package directions until al dente, reserving a splash of pasta water.
Season the diced chicken breast with half 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 remove from the pan and set aside.
In the same skillet, add the sliced cremini mushrooms and sauté until they release their moisture and become deeply browned.
Add the minced shallot and garlic to the mushrooms, cooking for 1 minute until fragrant.
Pour in the chicken broth to deglaze the pan, scraping up any browned bits from the bottom.
Return the chicken to the skillet and add the cooked tagliatelle, tossing everything together to coat.
Remove from heat and drizzle with truffle oil, then stir in the grated parmesan and fresh parsley.
If the sauce is too thick, add a tablespoon of the reserved pasta water to reach a silky consistency.
Season with the remaining salt and pepper before serving immediately in warm bowls.