Clean the mushrooms by wiping them gently with a damp paper towel or mushroom brush. Avoid rinsing them under water as mushrooms absorb moisture quickly, which will prevent proper crisping.
Trim the stems if they look dry or woody, then cut larger mushrooms in half or quarters. Keep smaller mushrooms whole for even cooking.
Preheat your air fryer to 380°F (193°C) for 3 minutes to ensure even cooking from the start.
Combine all seasonings in a large mixing bowl—Parmesan, garlic powder, thyme, paprika, salt, and pepper.
Add mushrooms to the bowl and drizzle with oil, then toss everything together until each mushroom is evenly coated with oil and seasonings.
Place mushrooms in the air fryer basket in a single layer with some space between pieces. Work in batches if necessary—crowding will create steam and prevent crisping.
Air fry for 8 minutes, then shake the basket or flip the mushrooms with tongs.
Continue cooking for 5-7 more minutes until the mushrooms are golden brown and crispy on the edges.
Transfer immediately to a serving dish. If using the optional ingredients, toss with fresh lemon juice and sprinkle with parsley while still hot.