Preheat oven to 150˚C.Put the first seven ingredients in a large roasting dish. Add the mushrooms and toss them in the liquid gently so they are well coated but do not break up. Make sure the mushrooms sit skin side down on top of the mixture and season with salt and pepper.
Cover with foil and bake for 60 minutes, basting the mushrooms every 20 minutes or so. Remove from the oven, lift the mushrooms out of the liquid and set aside to cool.
For the salsa:
Combine all ingredients in a small bowl. Season well and set aside.
For the filling:
Combine the feta, parmesan and harissa in a medium bowl with ± 5 tablespoons of the mushroom poaching liquid, stir until smooth and spreadable, then set aside.
For the pastry:
Preheat oven to 200˚C.Roll the puff pastry to a thickness of 5mm. Using a knife and a glass tumbler cut the pastry into discs just larger than the mushrooms. ± 10cm.Place the discs onto a baking tray lined with baking paper. Cut a border in each pastry circle about 2 cm in from the edge. Do not cut all the way through, you are just trying to create a little pastry border.
Bake the disks for 25-30 minutes until puffed up and cooked through. Remove from the oven and press the centre down of each pastry disc leaving the border puffed up. Add a spoonful of harissa cheese filling to each tartlet.Top each one with a whole portobello mushroom and squash it down to spread the filling.
Return tartlets to the oven for 5 minutes. Serve tartlets on a platter with dollops of fresh salsa and a crack of black pepper.