Preheat oven to 350° F.
Heat the olive oil in a large skillet over medium-high heat. Add the onion and cook, stirring often, for 2 minutes.
Add the ground beef to the pan and cook, crumbling, until browned. Drain off any excess grease.
Then add the chopped bell pepper and cook for 2 minutes, stirring often.
Add the chili powder, cumin, garlic powder, dried oregano, salt, pepper, corn, black beans and 1 cup of the salsa. Stir to combine. Remove the pan from the heat.
Spread the remaining ½ cup salsa in the bottom of a 13x9-inch baking dish.
Lay 4 of the tortillas in the baking dish, arranging them so that they cover the bottom of the dish as best as possible.
Spread ⅔ of the beef mixture over the tortillas and top with ⅓ of the shredded cheese.
Lay the remaining 4 tortillas on top, followed by the remaining beef mixture and then the remaining cheese.
Cover the dish with foil (first spray the underside of the foil with cooking spray to prevent the cheese from sticking to it). Bake for 25 minutes. Then uncover and bake for 5-10 more minutes, until hot and bubbly and cheese just starts to brown. Serve with toppings as desired.