Fish pie with a mild cheese sauce (bear in mind limited dairy allowance). Also beware of dairy if he may have an intolerance.
Poached or grilled fish or chicken with mash.
Macaroni cheese or mushy cauliflower cheese.
Hot pot with easy to mash stewing steak (maybe in the slowcooker?) in gravy with mashable veggies like carrots and potatoes without skins.
Soups which haven't got bits in them though you could include things he is allowed like pasta or soft meat and mushy veggies.
You could make your own nutritious veggie soups like carrot or watercress (just make sure it's blended well and bits removed).
Basically think simple foods, easy to mash up and therefore digest (be digested by stomach acids) and pass through the system.
Just seen on another sheet to avoid peas :(
Another good link...
http://www.northumbria.nhs.uk/page.asp?id=3065 00