Due to the concave bottom and central draining hole, the wort being recirculated through the pump will pass through the malt pipe and then down through the boiler false bottom. The wort would normally then follow the path of least resistance, making a b-line for that drainage hole.
What this Heat Exchanger Dish does is force that recirculating wort up to the edge of the BrewZilla base and pass over the elements for a longer period, this then aids in faster heating exchange with the wort, which can help you on a brew day reach those temperatures much quicker.