Bring a large pot of well-salted water to a boil. Cook the fettuccine until just shy of al dente, reserving 1 to 1 1/2 cups of pasta water before draining.

While the pasta cooks, heat a large skillet over medium-high. Add the butter. Once foamy, add the mushrooms in an even layer with a pinch of salt. Cook, undisturbed for 2–3 minutes, then stir and continue until they’re browned and their liquid evaporates, about 6–8 minutes total.

Reduce heat to medium. Add the garlic and cook 30–60 seconds until fragrant, not browned. Season with pepper.

Add the drained pasta to the skillet with 1/2 cup reserved pasta water. Toss to coat, then sprinkle in the goat cheese. Stir until it melts into a creamy sauce, adding more pasta water as needed to loosen.

Stir in lemon zest and 1 tablespoon lemon juice. Taste, then add more lemon, salt, and pepper to balance. If using, fold in Parmesan for extra savoriness.

Finish with parsley or red pepper flakes. Serve hot, with a final squeeze of lemon and a twist of black pepper.