Slice the tips off the tomatoes and use a spoon to hollow out a space inside them. With ripe tomatoes it'll be easy. If they're firmer, it helps to use a knife, but be sure not to damage the outer skin!
Cut three big circles in some pizza dough and place each one around a tomato. Press the edge of the dough tightly around the opening so it doesn't fall off.
Then fill the tomatoes with equal shares of ham.
Now put the mozzarella, olive oil, salt, and pepper in a bowl and purée them. Pour the same amount of this mix into each tomato, covering up the ham.
Finally, sprinkle the oregano over each tomato and bake them in the oven at 355°F for 20 min, with the air circulator on.