Bring a large pot of salted water to a boil and cook the tagliatelle according to package directions until al dente.
Reserve 1/4 cup of the starchy pasta water, then drain the noodles and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium-high heat.
Season the chicken breast pieces with half of the sea salt and black pepper, then sauté until golden brown and cooked through.
Remove the chicken from the skillet and set aside on a plate.
In the same skillet, add the sliced cremini mushrooms and cook until they release their moisture and become deeply browned.
Add the minced garlic to the mushrooms and sauté for 30 seconds until fragrant.
Return the cooked chicken to the skillet along with the drained tagliatelle and the reserved pasta water.
Drizzle the truffle oil over the mixture and toss everything together over low heat until the pasta is evenly coated and glossy.
Season with the remaining salt and pepper, then serve immediately topped with grated Parmesan cheese and fresh chopped parsley.