Preheat the oven to 375°F. Lightly grease a 9-by-13-inch baking dish.
Cut the three large bell peppers into roughly 1-inch pieces and spread them in the prepared baking dish. Drizzle with the olive oil, season lightly with Creole seasoning, and toss to coat. Bake uncovered for 10 minutes while preparing the filling.
Heat a large skillet over medium-high heat. Add the diced sausage and cook for 3 to 4 minutes, stirring occasionally, until it begins to brown. Transfer the sausage to a plate.
Add the ground beef and chicken livers, if using, to the skillet. Cook for 5 to 7 minutes, breaking the meat apart, until browned and cooked through. Drain excessive grease, leaving about 1 tablespoon in the skillet.
Reduce the heat to medium. Add the butter, onion, diced green and red bell peppers, and celery. Cook for 5 to 6 minutes, stirring occasionally, until the vegetables begin to soften. Add the garlic and cook for another 30 seconds.
Return the sausage to the skillet. Stir in the Worcestershire sauce, Creole seasoning, smoked paprika, garlic powder, onion powder, thyme, black pepper, and cayenne, if using.
Pour in the broth and simmer for 2 to 3 minutes, scraping up the browned bits from the bottom of the skillet.
Fold in the cooked rice, green onions, and parsley. Cook just until the rice is evenly coated and the liquid has been absorbed. Taste and adjust the seasoning. The filling should be moist but not soupy. Remove it from the heat.
Remove the baking dish from the oven. Spoon the dirty rice mixture evenly over the partially cooked bell peppers and gently press it into an even layer.
Sprinkle the cheddar and pepper jack evenly over the top. Cover the dish loosely with foil and bake for 20 minutes.
Remove the foil and bake for another 8 to 10 minutes, or until the cheese is melted and lightly browned around the edges. For a darker top, broil for 1 to 2 minutes while watching closely.
Let the casserole rest for 10 minutes. Garnish with chopped green onions or parsley and serve.