get some button mushrooms, remove the stalk, put a bit of pesto inside the upturned mushroom, top with grated cheese (I'd use a mature tasty) and grill.
Yummy finger food
I always like to buy Parmesan cheese in a block and grate it just before use. It retains it's flavour much better that way. If grated, you can store it in the freezer before use - it will keep significantly longer and still can be used straight from the freezer. It just needs to be stored in an air tight container.