Gently remove the stem from the mushroom.
For the filling, mix Japanese mayo, cream cheese, mozzarella, lemon zest, and black pepper. Mix until everything is combined. Rest in the fridge while you prepare the other ingredients.
Add eggs, flour, water, garlic powder, and paprika to a large mixing bowl. Mix until it becomes a thick batter consistency. Add more flour or water to adjust consistency.
Fill the mushroom with the creamy mixture, and coat the mushroom in the batter, then in panko. Using your hands, tightly press the panko to prevent it from falling off.
In a pot, heat oil enough to fully cover the mushroom. Once the oil is hot, add in the mushroom poppers, mushroom cap side down.
Deep fry the mushroom poppers for 2 minutes on each side until golden brown.
