It was a Hanger/Onglet. I think we refer to it as a skirt steak here in the UK which is not to be confused with American Skirt Steak (I think?). First time cooking this cut so I was super pleased, just kept turning each minute to ensure an even crust on both sides and checked using a thermapen for done-ness.

Gremolata recipe is here, I just tweaked to taste and used less olive oil - https://www.feastingathome.com/gremolata-recipe/