Open your Instant Pot and pour 1 cup of water into the liner. Insert your steamer basket or trivet, and place the broccoli inside. Put the lid on the Instant Pot and turn it to steam for 2 minutes. When the cook cycle is up, remove the lid, set the broccoli aside, and pour out the water.
Return the liner to your pot and put your Instant Pot to saute. Add the butter until it melts completely. Then add the minced garlic and saute until fragrant.
Add the chicken broth, heavy whipping cream, lemon juice, lemon zest, onion powder, oregano, thyme, and salt into the Instant Pot. Stir to combine.
Add the shells into the instant pot, making sure they are completely submerged. Set the Instant Pot to HIGH for 5 minutes. Once the pasta is done cooking, do an Instant Release.
Open the lid to the Instant Pot and add in the parmesan cheese. Stir to combine until the parmesan melts into the liquid. Then add the broccoli and stir again until combined. Salt again to taste if desired.
For best results, allow the pasta to sit for about 10 minutes so that the sauce thickens. Serve and enjoy!