Preheat oven to 180 degrees C. Grease a 12-hole muffin tin.
If you're using frozen meatballs, defrost them.
Roll out the pizza dough and cut into 7cm squares. (A pizza wheel cutter is great for this). Place one square of dough in each muffin cup of the muffin tin. Press the dough down into the form so the cup is lined with dough, and there's still a bit of overlap at the top - you'll need to overlap to close the puff later.
Drop 1 tablespoon or so of sauce in the centre of each cup lined with dough. Place a meatball on top of the sauce. Sprinkle mozzarella cheese on top.
Pinch the 'puff' closed by drawing up the 4 corners of the dough and pinching the dough together.
Baste the puffs lightly with olive oil and bake.
Allow to cool! These are very hot inside, especially for kids.
Check the baking temp and cooking time of the pizza dough recipe you're using. That's best to follow.
Before cutting all the dough, try assembling a single puff. It'll help you to get the idea of how big to make the dough and how much ingredients a puff can hold.