Preheat oven to 450˚F.
Toss the mushrooms with 2 tablespoons olive oil and season with salt and pepper.
Spread the mushrooms on a lightly greased rimmed baking sheet in one single layer.
Add the sprigs of thyme over the mushrooms.
Roast for 15 minutes; remove from oven and carefully drain out the liquid, if any.
Put mushrooms back in the oven and continue to roast for 15 to 20 minutes, or until all the liquid from the mushrooms has completely evaporated. Stir halfway through cooking.
Remove from oven and discard the thyme sprigs.
In a large bowl whisk together the remaining olive oil and the lemon juice; add mushrooms and toss to coat.
Stir in the parmesan cheese and nuts.
Taste for salt and pepper and adjust accordingly.
Transfer the mushrooms to a serving bowl and garnish with parsley.