Preheat oven to 200°C.
Heat the oil in a saucepan and sauté the onion. Add the spinach and 50ml water. Cover and steam for three minutes. Remove from the heat and once cool enough, squeeze any excess water from the spinach.
Knock the dough down and roll into four 20cm circles. Spread tomato paste over the circles, leaving a 2cm edge.
Put the spinach onto one half of each dough circle and sprinkle with the feta. Season with salt and black pepper and sprinkle the mozzarella over.
Brush the edge of the dough circles with a little water. Fold the open half of the dough over the filling and press the edges together. cut a slit in the top of the dough. Place on a baking sheet and bake for 15 minutes or until the dough is golden and cooked.