Prepare mushrooms: Wipe the mushrooms clean with kitchen paper. Depending on their size, halve or quarter them. If using Portobello, cut them into chunks. Make sure that the pieces are all of the same size so that they can cook evenly.
Spices: Place in a bowl. Add olive oil, garlic powder, 1 tablespoon lemon juice, salt, and pepper. Toss well to coat.
Preheat the air fryer, if required by its instruction manual; I preheat mine for 3 minutes at 190 degrees Celsius/ 370 degrees Fahrenheit.
Air fry: Place the mushrooms in the basket and cook for 10 minutes, shaking the basket halfway through. Check to see if they are done to your liking; you might want to add a couple of minutes, depending on the machine you are using.
Serve: Transfer to a bowl and adjust the taste with the remaining lemon juice, salt, and pepper. Sprinkle with chopped parsley and serve immediately as suggested above.