Preheat your oven to 375°F (190°C).
Wash the bell peppers and slice the tops off. Remove the seeds and membranes, creating a hollow space for the filling. Place the peppers upright in a baking dish.
In a skillet, heat the olive oil over medium heat. Add the finely chopped onion and sauté for about 3-4 minutes, or until it becomes translucent and fragrant.
In a large mixing bowl, combine the shredded cooked chicken, cooked rice, drained black beans, frozen corn, taco seasoning, and chunky salsa. Stir until everything is well combined and evenly coated.
Spoon the chicken and rice mixture into each bell pepper, packing it down gently.
Top each stuffed pepper with shredded cheddar cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes. Then, remove the foil and bake for an additional 10-15 minutes, or until the peppers are tender and the cheese is bubbly and golden.
Once out of the oven, let the stuffed peppers cool for a few minutes. Garnish with chopped fresh cilantro if desired, and serve warm with extra salsa on the side.