Here's what I do with cooked chicken and the children love it:
Melt butter and add a chicken stock cube. Stir until it is dissolved. Add about a tbsp flour and stir to a paste. Next add about a pint of milk and make a smooth sauce. Add the cooked chicken, some frozen peas and frozen corn. Heat through.
Make a pastry lid, or mashed potato topping and cook in the oven for half and hour or so.