Season chicken, boil water, and gather ingredients.
Sear chicken in olive oil until golden and cooked through.
Sauté onion, garlic, and mushrooms; deglaze with wine.
Cook tagliatelle until al dente, reserve 1 cup pasta water.
Add cream, butter, and Parmesan to skillet; simmer until creamy.
Return chicken and pasta; add spinach, basil, and pasta water as needed.
Stir in lemon juice, adjust seasoning, and serve immediately.