3/4 cup Parmesan cheese, grated, plus more for serving
1 Tbsp fresh chives, snipped
1 tsp salt
Bring a large pot of salted water to a boil and cook the penne for 8 to 9 minutes or until al dente.
While the pasta is cooking: In a small bowl whisk 1/4 cup olive oil, lemon juice and zest together.
Drain the pasta: reserve two cups of pasta water, set aside.
Place pasta back into the hot pot. Pour the lemon/olive oil mixture over the top and gently toss together until the pasta is evenly coated.
Heat a small amount of olive oil in a large skillet over medium heat and cook the pancetta, turning as necessary, until crisp and golden brown, about 7 minutes. Transfer the pancetta to a paper towel-lined plate to drain.
Add the shiitakes to the skillet with the pancetta drippings and cook over medium-high heat until browned and softened, about 5 minutes.
Add the garlic and cook for another minute or until fragrant and heated through. Transfer the shiitake mixture to the pot with the lemon noodles and set aside.
Add one cup of the reserved pasta water to the skillet and bring to a boil, scraping up any brown bits on the bottom. Add the asparagus and cook, stirring frequently, until bright green and crisp-tender, about 3 to 4 minutes.
Transfer the asparagus and any leftover liquid in the skillet to the pasta pot along with the Parmesan cheese, chives and salt.
Gently toss the contents of the pot together, adding more reserved pasta water as necessary to moisten the mixture.
Serve pasta immediately with a generous amount of pancetta crumbled over the top and additional Parmesan cheese to taste.