This is a duplicate of Launching Processing tool User Interface using PyQGIS. However, the answer provided is not correct for QGIS 3.4.1.
from processing.gui.CommanderWindow import CommanderWindow
results in a
ModuleNotFoundError: No module named 'processing.gui.CommanderWindow'
Anyone know the current syntax to launch a processing tool from pyqgis, so that I can call one from e.g. a plugin?