Combine the warm water, yeast, and sugar in a jug or large bowl. Whisk with a fork to dissolve the yeast.
Stand in a warm place for 10 minutes or it becomes frothy.
Sift the flour and salt into a large bowl. Add the yeast mixture and 2 teaspoons of olive oil. Mix to form a soft dough.
Turn the dough onto a lightly floured surface. Knead until elastic. About 5-7 minutes.
Place in a lightly greased bowl. Cover with plastic wrap. Let the dough stand in a warm place for 20 minutes or until the dough doubles in size.
Meanwhile, heat 2 tablespoons of olive oil in a large frying pan over medium heat.
Add the spring onion and cook, stirring, for 1 minute or until softened.
Add the mushrooms and cook, stirring occasionally, for 3 to 4 minutes or until softened. Add currants (if using) and spinach.
Cook for 1 minute or until spinach has just wilted. Season with salt and pepper.
Remove from heat.
Transfer the spinach mixture to a sieve placed over a bowl or the basin to drain excess liquid. Cool for 10 minutes.
Divide the risen dough into 8 equal portions. Roll 1 piece of dough into a 10cm x 15cm rectangle.
Combine both the feta and cheddar cheese in a small bowl. Use a table spoon to scoop spinach mixture over one half of the rectangle.
Top with the cheese mixture and fold the dough over to enclose the filling.
Press edges together to seal.
Repeat with the remaining dough, spinach mixture and cheese mixture.
Brush one side of each pastry rectangle with some olive oil and place in a large pan on a medium to high heat.
Cook for 2 to 3 minutes or until base is golden. Brush uncooked side with oil. Turn over.
Cook for 2 to 3 minutes or until golden and crisp.
Cut in half and serve with lemon wedges if desired.