Whisk flour, salt, and yeast together in a large bowl.
Heat milk and water to blood temperature and add, with oil, to flour.
Mix all together until combined in a rough dough.
Cover and stand for ½ hr.
Give it a very quick knead, cover again for 1 hour or until doubled.
Roll out into a large rectangle, roughly 50x40 cms.
Cut in half and place half the dough on a greased shallow baking tray.
Preheat oven to 220C.
Heat oil in fry pan, add bacon and spring onions, saute until bacon crisp. Remove and drain on kitchen towel.
Add mushrooms to same oil and saute until soft and cooked, sprinkle with oregano, add pepper to taste. Cool.
Sprinkle base of focaccia on the baking dish with the grated cheese, then sprinkle remaining ingredients over evenly.
Gently cover with other half of dough and pinch edges together.
Dimple top of dough with your knuckle, drizzle with extra virgin olive oil and sprinkle with sea salt.
Bake for 20-25 minutes. Remove from baking pan and cool on rack.