Step 1: Preheat your oven to 400°F (200°C). Prepare a baking dish by lightly greasing it or lining it with parchment paper.
Step 2: Halve the Anaheim peppers lengthwise and carefully remove the seeds and membranes. Place the pepper halves cut-side up in the prepared baking dish.
Step 3: Heat olive oil in a large skillet over medium heat. Add the diced onion and cook until softened, about 3-4 minutes. Add the minced garlic and cook for another minute until fragrant.
Step 4: Stir in the cooked shredded chicken, cooked rice, black beans, corn, chicken broth, chili powder, cumin, oregano, salt, and pepper. Cook for 5-7 minutes, stirring occasionally, until the liquid has mostly absorbed and the mixture is heated through.
Step 5: Remove the skillet from heat and stir in half of the shredded cheese (1/2 cup).
Step 6: Carefully spoon the chicken and rice mixture into each Anaheim pepper half, mounding it slightly.
Step 7: Cover the baking dish with foil and bake for 20 minutes. This allows the peppers to soften and the flavors to meld.
Step 8: Remove the foil, sprinkle the remaining 1/2 cup of cheese over the stuffed peppers. Bake uncovered for an additional 10-15 minutes, or until the cheese is melted and bubbly and the peppers are tender.
Step 9: Remove from the oven and let rest for a few minutes before serving. Garnish with fresh cilantro if desired.