Bring a large pot of salted water to a boil and cook the tagliatelle according to package instructions until al dente.
Season the chicken breast with half the sea salt and black pepper, then sear in a pan over medium-high heat until cooked through.
Remove chicken from the pan, let it rest for 5 minutes, then slice into thin strips.
In the same pan, add the olive oil, minced garlic, and finely chopped shallots, sautéing until fragrant and translucent.
Add the sliced cremini mushrooms to the pan and cook until they are golden brown and tender.
Drain the pasta, reserving 2 tablespoons of the starchy pasta water.
Toss the pasta, chicken, and reserved water into the pan with the mushrooms.
Drizzle with truffle oil and sprinkle with parmesan cheese, tossing well to create a light, glossy sauce.
Garnish with fresh parsley and serve immediately.