Mushrooms with stilton, spinach and walnuts (served by itself or as an accompaniment to steak)

Currently (along with the entire planet it seems), we are eating healthly and exercising more in a a bid to be a God and Goddess this summer. Apparently 'skinny' is out and 'warrior' is in, so there is hope at last! I passionately despise 'diets'. but do believe in changing eating habits. The one thing I know that works for me is lowering my carb intake. Based on this our dinner last night, inspired by Nigel Slater, was a mushroom based dish, accompanied by a beautifully rare piece of rump, which are 7 year old gatecrashed, the carnivore that he is!

Ingredients
6 large flat mushrooms
1 garlic clove chopped
pinch of thyme
knob of butter
water
handful of spinach
stilton cheese
walnut halves
(Optional to serve with or without meat)
slice of rump steak cur 1 inch thick
half a lemon
splash of marsala or red wine

Take your rump steak out and place on a plate to come to room temperature. Rub the steak both sides with a little olive oil. Season quite generously with coarsely ground black pepper and sea salt.
Using a large saute pan with a lid, heat the butter and when melted put in the mushrooms, stalk side up. Let them begin to cook and sprinkle over the chopped garlic and pinch of thyme. season and add a splash of water. Put the lid on and allow this to cook gently, spooning over the garlicky, herby liquid from time to time. As these are cooking, heat a frying pan until white hot. I like my steak rare, so I would give it 2 minutes per side, then allow to rest whilst having a squeeze of lemon over it.
Put a small amount of stilton in each mushroom (you only need a small amount for flavour), scatter over the spinach and walnuts and put the lid back on.
Whilst the cheese is melting and the spinach melts, deglaze the steak pan with a splash of marsala or wine, and pour over the resting meat.
Simply delish, and as long as you are scant with the butter, and stilton (walnuts are rich in alpha linolenic acid which has many nutritional and health benefits including anti-inflammatory and anticancer properties), then believe it or not, this is diet food!

Just one more thing; one of the things we need to be doing is eating food that keeps us satiated. This is low GI food, so therefore takes longer to convert to energy, so there is less chance of surplus unused energy which would become fat. Bonus.