Heat oven to 325°F.

Wipe mushrooms clean and remove stems. Toss mushroom caps with olive oil, salt, and pepper and place in a single row on a baking sheet. 

Combine mushroom stems, garlic, parsely, scallions, walnuts, in a food processor. Pulse until finely minced, but not a paste. 

Heat a large frying pan over medium heat. Remove chorizo from it’s casing and cook, breaking up with the back of a wooden spoon until starting to brown. Add mushroom stem mixture and cook another 1-2 minutes. Remove from heat and stir in Cotija cheese. 

Divide filling evenly between mushroom caps and bake until mushrooms are tender and filling is browned about 40 minutes. 

Transfer to a serving tray, sprinkle with parsley and more Cotija and serve.