You will need
Adjust oven rack to the middle position. Preheat the oven to 160°C.
Wipe the rounded sides of the mushrooms with a damp cloth. Place into a smallish ovenproof dish, stems pointing up. Season. Cut a very small hole in one of the top corners of the Basil Pesto pack and squeeze a thin ring of pesto into the mushrooms.
Bake open for 30 minutes.