Cheese and fruit... such a natural combination. Adding a little sweetness to a gooey grilled cheese brightens it up and makes it surprising. If you add pears or apples, slice them very thin so that they get slightly soft from the heat of the pan.
Other options: a smear of fruit jam, some chopped, dried fruit, or even (stay with us here) a sprinkling of brown sugar in between slices of a mild-flavored cheese.
Does this sound good to you? What are you planning for lunch?