Salmon with Pea & Celeriac Mash

I was looking for a new way to cook salmon and found this recipe using an ingredient I'd never heard of before.
I decided to give it a go.   So now I'm going to share it with y'all!

Start by preparing your celeriac.  This what it looks like pre-prep.  You only need 350g/ 12oz so you only need a small one.  Slice the side with little shoots coming out so that it has a flat surface to rest on.  I didn't take a picture of it before I did this, but they looks sort of like spring onions.

Peel it by slicing the outer skin.  It cuts pretty easily, but you'll need a knife rather than a peeler as the skin is thick and rough.  This is what it will look like once that's done.

Cut the whole thing up into cubes.  It has an interesting texture- soft and almost spongy.

Peel and cube 1 floury potato.  

Chuck the potatoes and celeriac in a pot of water and put on to boil.  While it's cooking,  line a cooking sheet with alumin(i)um foil and put the grill (in the US- the broiler) on a medium heat.  Curl the edges up so that it traps any juices that are made during cooking.  Rub some olive oil on the foil to keep the fish from sticking.

Put the salmon fil(l)ets on the foil and spread about 1 tsp. of whole grain mustard on each fi(l)et.

Squeeze the some lemon juice over the top of the salmon.

Once the pot has been boiling for about 5 minutes, put the salmon under the grill (broiler) for about 15 minutes.  Once 10 minutes have passed, add 140g of frozen peas to the boiling pot.

After 5 more minutes, drain the water and put the whole mess back in the pot and mash it up so that it all mixes together and the peas start to break a little.  The timer for the fish will also start bleeping, so take the fish out (duh).  Add some salt and pepper to the mash if you like.

Spoon the mash onto the plates.

Put the salmon across the top of the mash and serve!

The meal turned out tasty, but maybe slightly bland.  I'm not sure what I'll try next time to add a little somethin' somethin' to it.  Any suggestions?
Have you ever been bold and used a scary looking ingredient?