These could also be used as a main course.

I adapted this recipe from one I saw on the Australian Women's Weekly "Fresh" TV show.
Here is the original recipe.

My version:

About 200g (roughly ½ pound) beef mince (aka ground beef)
1 egg
Sprinkle of onion powder
Generous sprinkle of dried oregano
About (I didn't exactly measure) ¼ cup each mozzarella and parmesan cheese
About 20 green olives.

Remove olive seeds. Mix all other ingredients together and stuff into olives. (It looks kinda like little meatballs with little green coats)
Bake in a hot oven until browned. Time will depend on the size of the meatballs. Mine took about 15 minutes. You could also cook them under a griller (okay, a broiler if you're a foreigner ).