Preheat oven to 350 degrees. Heat the oil in a large skillet over medium high heat. Add the onion and saute until just tender, about 5 minutes. Add the ground beef and cook until browned, breaking it into little pieces as it cooks, about 6 minutes.
Add the taco seasoning and corn and stir gently to combine, allowing to cook for an additional 2 minutes. Remove from heat.
Take each sweet pepper and slice it lengthwise, removing 1/3 of the flesh. Remove the seeds and veins, then fill with a teaspoon or two of rice, followed by 1/2 teaspoon of salsa, then top with the beef mixture. Using a casserole dish, or foil-lined baking sheets, place the stuffed peppers in a row until full, then sprinkle with the cheese.
Bake for 30 minutes, or until the cheese is melted and just slightly browned, and the peppers are softened. Allow to cool for a few minutes, then server immediately.