Possible Clues:

• Mushroom from Asia
• Possible zucchini stuffing
• Mushroom added to udon soup
• Tiny-capped mushroom
• Oriental mushroom; E ikon (anag.)
• Small-capped mushroom
• Edible Japanese mushroom
• Mushroom in Japanese cuisine
• Edible mushroom of Japan
• Type of mushroom used in casserole? No kidding