Dissolve the yeast and the sugar in the warm water and let sit for 10 minutes. Add half the flour, the salt, two tablespoons olive oil and stir. Place the dough on a floured surface and gradually knead in the remaining flour. Knead until dough is smooth, about 10 minutes.
Transfer the dough to an oiled bowl and cover with a damp cloth. Let rise until doubled in size, about 1 hour.
Preheat oven to 200 degrees C.
While the dough is rising, make the topping. Heat the two tablespoons olive oil in a large frypan and saute the onion until softened. Add the chicken, passata and basil. Season with salt to taste and cook until heated through.
Roll out the pizza dough and place on a pizza tray. Spread the chicken mixture over the dough and sprinkle the grated mozzarella on top. Sprinkle with oregano to taste, garnish with the olives and bake 15 minutes or until the base is done.