Preheat oven to 205 °C (400 °F).
Remove the mushroom stems (be careful not to break the caps). Mince the stems.
In a bowl, mix the cream cheese with the minced mushroom stems. Add salt and pepper to taste. Fill the mushroom caps with a spoonful of the mixture.
Line a baking sheet with parchment paper, and place the stuffed mushroom caps on the baking sheet. Sprinkle the Panko on the mushroom caps. Cook in the oven for 15 to 18 minutes, until golden.
The spicy version: Replace the mushrooms with 6 jalapeño peppers, seeded and cut length-wise. Stuff each jalapeño half with the cream cheese, sprinkle with Panko, and cook as you would the mushrooms!