Pre-heat the oven to 200C (180C fan forced)
Either with a rolling pin or by hand, roll or stretch one of the dough balls to fit the base of the baking tray. Place the sheet of dough into the tray.
Spread the cooled mushrooms over the dough, leaving a clear 2cm edge on each side of the dough.
Sprinkle the cheese over the top of the mushrooms.
Roll out the remaining dough ball to fit the baking dish and carefully lay this over the top of the cheese.
Crimp the two pieces of dough together.
Dimple the top of the focaccia with your fingers. Drizzle olive oil over the top of the focaccia and sprinkle with sea salt.
Cook for 30 - 40 minutes until the focaccia is golden brown.
Remove from the oven and slide the cooked focaccia from the baking tray onto a board or rack.
Cut into pieces and serve.