what makes the 'Lehrer' plural?
Take note of the 'Die' and the 'essen'. At singular it would be: Der Lehrer isst Sandwiche.
Here are correct forms for teacher:
indoctrinator Lehrer m
instructor Lehrer m
schoolmaster Lehrer m
teacher Lehrer m; Lehrerin f
Tricky one :U
the word 'Sandwiche' at the end was inaudible/too robotic. I had to skip because I just couldn't hear what it was.