Peel celeriac (saving the leafy top) using a paring knife and cut into ⅛ inch slices, then cut those slices into long thin match sticks (if using celery, just slice thinly). Place in the bowl with the lentils.
Cut the apple the same way, into long match sticks, leaving the peel on. Place in the bowl.
Finely dice the onion, place in the bowl.
Slice the celeriac stalk or celery stalk, add to bowl.
Add half of the chopped Italian parsley, saving the rest for garnish.
Mix all dressing ingredients in a small bowl incorporating the honey, remembering to toast the cumin seeds until fragrant. Fold the dressing in with the lentil mixture. Let sit 15 minutes before serving to allow the flavors to meld.
Adjust salt and pepper if necessary, adding more to taste. Add cayenne if you like.
To serve, place in a bowl or platter, scatter with fresh Italian parsley.