Heat about 1 tbsp. of olive oil in a large frying pan over high heat (you can eyeball the amount of olive oil).
When the pan is smoking, add the sliced mushrooms.
Let the mushrooms sit for a couple of minutes until brown on the bottom, and then flip.
When mushrooms are brown on both sides, remove them from the pan and set them on a plate for the time being.
Turn the heat down to medium and add another generous tablespoon of olive oil to the same pan.
Now add the sliced leeks.
Stir leeks until wilted and soft (about 8-10 minutes).
Add the browned mushrooms back to the pan and season with sea salt and thyme.
Remove from heat and serve.