Boil a large pot of salted water over high heat and cook the uncooked pasta according to package instructions, usually around 8-10 minutes, until al dente.

In a large skillet over medium-high heat, add olive oil and 1 tablespoon of butter. Add the onion and mushrooms, sautéing for 8-10 minutes until onions are translucent and mushrooms are browned.

Reduce heat to medium, stir in the remaining butter, garlic, and Dijon mustard. Cook for 1 minute until fragrant.

Pour in the broth, lemon juice, and zest, allowing to simmer for approximately 1 minute.

Remove from heat and stir in parmesan cheese and parsley. If too thick, adjust with reserved pasta water.

Drain the pasta and add to the skillet, tossing to coat with sauce.

Serve immediately, garnished with additional parsley if desired.