Grease a large round baking dish or line it with parchment {for easy torta removal after baking}.
Spread a layer of sauce on one tortilla and place it in dish.
Top with 1/2 of pork and drizzle with more sauce. Top with another tortilla.
Top second tortilla with 3/4 of the onions and corn and sprinkle with 2/3 cup cheese. Top this with another tortilla.
Place remaining pork on tortilla and drizzle with more sauce. Top with final tortilla and brush or spray top with olive oil. Cover and refrigerate before baking.
Preheat oven to 350 degrees. Bake torta, covered for 30 minutes.
Remove cover and continue to bake for 15-30 minutes, until torta is heated through. Garnish with reserved onions and cheese. Carefully lift torta out of dish and place on cutting board. Cut into wedges to serve.