Peel the garlic and ginger. Grate the ginger.
Peel the pear and the onions.
Place all the sauce ingredients in the food processor or blender and blend until smooth.
Trim the beef cheeks of as much fat as possible.
Pour the sauce mixture in to the bowl of the pressure cooker and then place the beef cheeks on top and submerge them a little - you want to ensure that the sauce is always in contact with the bottom of the bowl.
For an electric pressure cooker, close the lid and seal the vent. Use the manual option to set to high pressure for 75 minutes and then set it to start.
For a stovetop pressure cooker, lock the lid in place. Over high heat, bring to high pressure. Reduce the heat just enough to maintain high pressure, and cook for 70 minutes.
Towards the end of the cooking time, slice the mushrooms and then brown them in a pan with some oil. Slice the green onion in to thin slices, wash the coriander and pick the leaves to use as a garnish.
Once the beef cheeks have finished cooking, allow the pressure to release naturally for 10 minutes and then release any remaining pressure (for a stovetop pressure cooker, you can do this by running it under cold water. Do not do this for an electric cooker!)
Remove the beef cheeks and set aside. If necessary cut in to smaller pieces depending on how many serves you would like.
To serve, place beef cheeks in serving bowls with mashed potato. Pour the gravy around the beef cheeks and potato, place mushrooms and garnishes on top.