Preheat your oven to 400°F (200°C) to prepare for the casserole.

In a small bowl, combine the chili powder, cayenne pepper, garlic powder, smoked paprika, onion powder, ground cumin, dried oregano, salt, and black pepper. Stir thoroughly to blend.

In a 9x13 baking dish, mix together the chopped white onion, diced red bell pepper, and uncooked brown rice. Sprinkle the seasoning mix and stir until well-coated.

In a separate bowl, whisk together chicken broth, chopped green chilies, olive oil, and tomato paste until combined. Pour over the rice and vegetable mixture, stirring gently.

Fold in corn kernels, drained black beans, and shredded cooked chicken. Mix until evenly distributed.

Cover the baking dish tightly with aluminum foil and bake for 65-70 minutes.

Remove foil and sprinkle shredded cheddar over the casserole. Return to the oven for 5-10 minutes until cheese is bubbly and golden.

Let cool slightly, then serve topped with fresh cilantro, green onion, avocado slices, and salsa.