Place the self-raising flour in a bowl. Add the salt, oregano, oil, and boiling water. Mix with a fork until combined. Then knead with your hands. Let rest for 20 minutes. Meanwhile, mix the ingredients for the filling. Roll out the dough on a floured surface. Line the bottom and sides of the oiled skillet. Pour in the filling. Cover and cook over medium heat until fully cooked. Unmold. Top with the diced tomatoes and basil leaves. Drizzle with olive oil.