Place the oil in the Instant Pot and select “Sauté”. Then add lamb shanks, tomatillos, peppers, garlic, cumin, thyme and salt and cook for about 3-4 minutes.
Select “Cancel” and stir in broth.
Secure the lid and cook under “Manual” and “High Pressure” for about 15
Select “Cancel” and carefully do a Natural release.
Remove the lid and with tongs, transfer lamb shanks into a bowl.
In the pot, add cilantro, fish sauce and lime juice and with a hand blender, blend the mixture until pureed.
Return lamb shanks into pot and stir in the pureed mixture.