Set a griddle pan on the stove to heat, if you don’t have one, use a frying pan instead.
Season the steak and the mushroom with a little salt, pepper, a little of the olive oil and scatter over the thyme leaves.
Grill the steak for 2 minutes per side (rare) longer of you want it medium / well done. Then set it aside on a warmed plate to rest whilst you grill the mushroom.
When the mushroom is cooked, slice this and slice the tomato.
Your steak will now be rested, slice the steak on a bit of an angle so you have little finger thick slices. Butter the bread and place the tomato on the bottom slice, then build up the layers. We like to sandwich the steak with a little cheese above and below it, then topping with the mushroom and green sauce. Finish with the final layer of bread and pop the whole thing onto the still hot grill and toast it up a little. Then slice and devour!
Slice the sarnie in half and serve with more green sauce and whatever you fancy on the side, we like little roasted new tatties, with plenty of rosemary, salt and pepper and a nice cold beer!