Quick and delicious, good to have on hand:
No recipe - we don't need it. Wing it:
use onions if you wish, use leeks if that is what you have.
Olive Oil (or alternative) - a bit of thyme, salt and pepper, a touch of sherry or Marsala (either one is wonderful). Cremini Mushrooms or Oyster Mushrooms? Whatever you have.
Make enough so you can add them to your panini, top some rice, quinoa, pizza or pasta with them, make an omelette or frittata using them... How much easier can it get?
(It will also keep in your fridge for a few days)