Preheat the oven to 375°F.
In a large skillet, heat the olive oil over medium heat. Add the ground beef or turkey and cook until browned, breaking it apart with a spoon, about 5-7 minutes. Drain excess fat if necessary.
Stir in the cooked rice, black beans, corn, taco seasoning, and salsa. Mix well and cook for an additional 3-5 minutes until heated through. Season with salt and pepper to taste.
While the filling is cooking, prepare the bell peppers. Cut the tops off the peppers and remove the seeds and membranes. Place the peppers upright in a baking dish.
Spoon the taco filling evenly into each bell pepper, packing it down slightly. Top each stuffed pepper with shredded cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the peppers are tender and the cheese is bubbly and golden.
Remove from the oven and let cool for a few minutes. Garnish with fresh cilantro or green onions if desired before serving.