Advice Needed on feeding my 19yo son

I have just moved back in to the family home after 5 years away and have found my son living on rice and cheese.  He has always been difficult to feed having the usual aversion to vegetables, onions and anything that isn't neutral in taste, texture and colour.  However his diet is now particularly unhealthy and he eats huge quantities of the same thing every day.  I really need some advice on recipes which will vary his diet whilst keeping to his bland colour and taste palette.  I am finding it very difficult to wrap my head around this kind of food so any advice would be helpful.  Thanks for reading