For the Chocolate Lava: Stir together cocoa powder, honey, coconut milk and salt in a small saucepan. Cook over medium heat, stirring, until the chocolate is melted. Bring mixture to a low boil, stirring occasionally, for 5 minutes.
Remove the pan from heat. Add the dark chocolate and 1 teaspoon vanilla extract, stirring until smooth. Set aside. Any leftover sauce can be refrigerated and reheated.
For the Shake: Take the can of full-fat coconut milk out of the fridge. Scoop the thick coconut cream from the top (about 1/2 cup) and set aside. Reserve the coconut water for another use or for the shake.
Add the reserved coconut cream, 1/2 cup almond milk (or reserved coconut water), matcha powder (start with 1 tablespoon), the remaining 1 tablespoon vanilla extract, avocado, banana, spinach, almond butter, and a pinch of salt to a high-powered blender.
Blend until completely smooth and creamy, about 1-2 minutes. Add the remaining 1/4 cup of almond milk if needed to reach desired consistency.
To serve, drizzle the warm chocolate lava sauce into two glasses. Pour the matcha shake mixture over the chocolate. Top with cocoa nibs if desired.