Dice the onion and roughly chop the garlic. Add the oil to the Instant Pot and press the saute function. First, add the onion and saute until soft. Then add the lamb (raw or cooked) and then the garlic. Keep stirring until the meat is seared (if raw) and the onion is softened.
Roughly chop the carrot and butternut squash. Stir through the ras-el-hanout spice blend and tomato purée. Add the carrots, squash, canned tomatoes, cinnamon stick, sea salt, stock cube and 1 liter of water (or enough water to just cover the meat).
Cover and set the vent to ‘sealing’ and pressure cook for 25 minutes at high pressure. Allow for 10-15 minutes natural pressure release. Remove the cinnamon stick. Taste, and add more spices and season if needed. If the sauce is quite thin, sauté without the lid for a further 20-30 minutes to allow the liquid to reduce and thicken.
Roughly chop the cilantro and pistachios. Ladle into bowls. Garnish with the cilantro, pistachios and a sprinkle of chili pepper flakes. Serve hot.