What is This Metal Flashing and Hollow Space Where Top Plate Should be
At one time that metal piece was probably part of a vent pipe to transition a range hood up through the ceiling. If it had been in use there was likely to have been a rectangular to round transition that then piped out through a shrouded roof vent.

Just drilling a hole through the bottom of that metal piece may require a special treatment such as a grommet to protect the electrical wire from the sharp metal edges.