Toronto pizza is a pizza where the cheese goes under the ingredients, as a foundation, rather than on top, as a garnish, where it would melt and partially obscure the ingredients.
Putting the cheese underneath doesn’t happen in America or Australia, and it doesn’t happen in other parts of Canada, such as Montreal, Vancouver, Ottawa, or Whitehorse.
So much pizza is sold by the slice in Toronto, on display in cabinets and then heated as you order it, that putting the cheese underneath may have evolved as a way to better display the toppings by putting them on top of the cheese (though this doesn’t explain why this didn’t evolve in New York, the pizza slice capital of the world.)
Even the frozen pizzas sold in Toronto have the ingredients on top, to better show them off through the cellofilm window in the box in the freezer.
In Toronto, only some Greek-run pizzerias put the cheese on top.