Set Instant Pot to Sauté and adjust to “More” and add oil.
Pat lamb shanks dry and season with salt and pepper. Once the Instant Pot is hot, add lamb and cook until browned all over, about 4 minutes per side. Remove from pot and place on a plate. (You’ll likely need to do 2 at a time, adding more oil in between if needed, so you don’t crowd the pot).
Add garlic to pan and sauté, stirring, until fragrant, about 15 seconds. Add wine and cook 2 minutes, being sure to scrape the bottom of the pot to loosen browned bits. Stir in tomatoes, basil and oregano; cook 2 minutes.
Return lamb to pot, place the lid on and seal. Little sauce on top. Cook high pressure for 45 minutes. Allow the pressure to naturally release for 15 min before manually releasing the remaining pressure.
Serve lamb over polenta or mashed potatoes, sprinkling fresh parsley over top if desired.
If desired, you can remove the lamb shanks from the Instant Pot after cooking, and use the Sauté function to reduce the sauce for a few minutes to get a thicker sauce. Be sure to stir so the sauce doesn’t burn!