De or het lunchsessie?

The correct Dutch article is:

de lunchsessie

Rule Words ending in -tie and -sie: almost always de. See the rule

How to use lunchsessie

the lunchsessiede lunchsessie
this lunchsessiedeze lunchsessie
that lunchsessiedie lunchsessie
our lunchsessieonze lunchsessie
your lunchsessiejouw lunchsessie
every lunchsessieelke lunchsessie
which lunchsessie?welke lunchsessie?
a big lunchsessie / the big lunchsessieeen grote lunchsessie, de grote lunchsessie