I always new that a full valve guitar amp generates
heat but i didn't ever think it was enough to toast a slice of bread.I heard that there was this guy who opened up his amplifier and put a grill inside,he put 2 slices of bread in and closed it.he played guitar for around 20 minutes.After that he opened it up to find that the slices toasted well.I don't now if this can be realy true,can it?

You already posted this once.

that would never work. it wouldn't toast evenly or it would burn.