Tuna and sweetcorn pizza

Preheat the oven to 220ºC/200ºC fan/gas 7. Put both sachets of pizza mix in a bowl and pour on 200ml warm water (just warmer than your skin). Mix to make a pizza dough. 
Put on a lightly floured work surface and knead for 5-10 mins. Roll out to a 22cm x 30cm oblong and put on a large baking sheet. Brush the surface lightly with the oil, cover loosely with clingfilm and leave in a warm place for 10-20 mins to prove. Remove the clingfilm and spread the dough with the tomato pizza topping. Add the tuna, olives, onion and sweetcorn, distributing everything evenly. Sprinkle with the cheese and bake for 20 mins. Leave for 1-2 mins before slicing with a knife or pizza cutter.