I'm skoffelling through my dusty brain files trying to remember where I read this, but I just can't recall the source of this brilliant tip. Here it is: instead of wasting electricity and time re-heating a shop-bought pizza in a conventional oven, put a large frying pan on the heat. Add the pizza, crust-side down, into the dry frying pan (don't add any fat). Now cover with a tight-fitting lid. Leave for 3-7 minutes (depending on the ferocity of the heat). Take off the lid. Use a spatula to check whether the crust is golden, crispy and cooked. If it isn't, cook, covered, for a few minutes longer, by which time the topping will be nicely molten.
That's it - perfect reheated pizza. Ok, the topping won't be browned, but teens and tweens don't care about that. All they want is a crisp, snappy bottom (har) and a voluptuous, sizzling, cheesy topping (har har).