Memory uses the last-ramped level, so ramp to what you want. Specifically: Ramp down to moon, then turn it off. After that, a single click turns it on at moon level.
Or use the hold-from-off shortcut to access moon directly. But it doesn’t remember levels accessed from a shortcut.
Or leave the light in lockout mode, which works as a momentary moon mode.
Or in the most recent builds (which probably aren’t shipping yet), there’s a way to manually set the memorized level, so a single click from off will always go to that level.