Grease a 9 inch square cake pan.
Combine the butter, flour, sugar, baking powder, salt, milk and vanilla in a medium bowl.
In another bowl mix the brown sugar and cinnamon.
Add the peaches and apples to the brown sugar and mix to coat.
Spread the fruit evenly in the pan.
Pour the batter over the fruit and spread to coat the whole top.
Preheat the grill.
When the grill is hot, turn it to low.
Place the pan on the grill and cook for 15-20 minutes.
Remove from grill and serve warm.