Take out an 8-inch springform pan, or line an 8-inch cake pan with parchment paper, leaving plenty of overhang on the sides to help you lift the cheesecake from the pan once finished. Set aside.
Place pecans and oats in the bowl of a food processor or high powered blender, and blend until they resemble the texture of cornmeal. Add all remaining crust ingredients, and pulse to combine.
Pour the mixture into the springform pan, and use your hands to evenly spread it out to the edges of the pan. Use your fingers to press down firmly, making a thin, even layer of crust. Place the pan in the fridge while you make the filling.
Drain your soaked cashews, then add them and all remaining filling ingredients to the bowl of your food processor or high powered blender. Blend on high until completely smooth.
Pour filling into the prepared crust, and place in the fridge for at least 3 hours, or the freezer for 1 hour to firm up. At this point, the cheesecake can be covered and left in the fridge for up to 5 days before serving.
When ready to serve, place elderberry syrup, blueberries, ginger, and cinnamon into a small pot on the stove. Heat on high until boiling, then turn to low and let simmer for 5 minutes. Turn off the heat and add the chia seeds and honey, stirring to combine, and let sit for 5 minutes to thicken.
Serve each slice of cheesecake with a spoonful of warm berry sauce. Leftover sauce can be stored in a container in the fridge for up to 5 days, and gently reheated again before serving.