Press the "saute" button to get the Instant Pot heated up (make sure it's on "normal" heat).
Chop veggies: dice onion very finely, cut asparagus into 1-inch chunks (throwing away the tough ends), and mince garlic. You'll need about 1 1/2 cups of asparagus once chopped.
Melt 2 tablespoons of butter in the heated Instant Pot, then add onions and saute for 3 minutes. Add rice and saute for another 3 minutes, until just barely starting to toast. Press "cancel" to turn off the saute function.
Add the broth, lemon juice, oregano, salt, and veggies. Scrape the bottom a bit to make sure no rice is stuck. Place the lid on the pot with vent closed, and use "Manual" on high pressure. Select 6 minutes.
Once the rice finishes cooking, do a quick release by carefully opening the vent to release steam. After the pin drops, open the pot and carefully stir in the parmesan cheese.
Serve warm and garnish each serving with a few pinches of lemon zest.