Place the flour, yeast, sugar and salt in a large bowl. Stir together to combine.
Add the warm water and vegetable oil to the bowl and stir together to form a rough dough. Tip the contents of the bowl out onto a work surface and knead together, dusting lightly with extra flour as needed to prevent it sticking to the surface (just try to add as little extra flour as possible). Knead for about 10 minutes - the dough will be slightly sticky and quite soft but should be stretchy and smooth. You can also use a stand mixer with the dough hook fitted to knead it if you'd like.
Pour a little extra vegetable oil into the bowl you were using. Place the dough in and turn to coat with oil. Cover with a clean tea towel and leave somewhere warm for 1 hour to rise until doubled in volume (I place it in my oven, turned off, with a baking tray full of boiling water on the rack below - it makes the perfect warm, steamy environment for the dough to rise in).
Once the dough has risen, tip it out onto your work surface and pat out into a large rectangle. Sprinkle the baking powder all over the surface of the dough, roll it up, and then knead for 5 more minutes so the baking powder is incorporated.