Add all ingredients except for the plum and coconut sugar in a small blender or food processor. Blend until smooth or mostly smooth. Alternatively, you can use oat flour or instant oats and stir everything in a bowl. It just depends on your preference in texture of the oats.
Place blended mixture into a large ramekin. Place sliced plums on top. Sprinkle coconut sugar over the plums. Tightly cover the ramekin with a piece of foil.
In the bowl of your pressure cooker, add 1 cup of water. Place the trivet inside and set your ramekin on top of the trivet. Cover with the lid and make sure the valve is in the sealed position. Cook on high pressure for 15 minutes, then do a natural release for 3 minutes. Then release the remaining pressure. Using oven mitts, carefully remove the ramekin out of the pressure cooker and remove the foil. Enjoy warm! I topped mine with extra yogurt and cinnamon.