tablespoons lemon zest, about 1/2 lemons worth per tablespoon
salt and pepper
Bring large pot of salted water to a boil.
While water boils, heat 1 tablespoon olive oil in medium skillet. Saute onion until soft; add garlic and saute additional minute. Remove from heat.
Add pasta to boiling water and cook according to box directions. 2 minutes before cook time is up, reserve 1 cup pasta water, then add asparagus to boiling pot. Continue to cook until pasta is al dente. Drain cooked pasta and asparagus. Return pasta and asparagus to the pot, add 1 tablespoon olive oil, onion and garlic mixture, grated cheese, lemon zest and 1/2 the reserved pasta water. Season with salt and pepper, and stir gently until well mixed. Add additional pasta water as needed for desired consistency.