Peel the avocado and discard the pit. Blend all ingredients until completely smooth. Feel free to blend in a few coconut milk ice cubes for a super thick and ice-cream-like shake if desired. (To make coconut ice cubes, just freeze canned coconut milk in an ice cube tray. Do not add regular ice cubes, because that would dilute the flavor of the smoothie.) Serve cold. Leftovers can be covered and refrigerated for up to 3 days. The recipe makes about 2 cups.