Whatever you do don't pressure him.
Ignore the fact that he's only eating bread and cheese with some fruits thrown in.
I had a child who had a very very narrow range of foods that he'd eat. You could count them on one hand.
Now, I always believed that a hungry child will eat anything, but no, it doesn't work like that.
In the end it was suggested that he should be checked out by a pediatrician, who pronounced him healthy and a lovely little boy.
I was told, to go away and ignore it and it would come right in the end.
I did and it was.
He gradually, over the years, added more food to his repertoire and now he eats pretty much everything.
It didn't happen over night though, but I never, never pressured him. And made sure no one else did either.