Start by gathering all your ingredients. Make sure the shrimp is peeled and deveined, the sausages are cut into rounds, and the rice is cooked. Preheat your oven to 350°F (175°C) while you prepare the rest of the ingredients.
In a large skillet, melt the butter over medium heat. Add the minced onion, diced green and red bell peppers, and minced garlic. Sauté for about 5-7 minutes until the vegetables are tender and fragrant. Next, add the andouille sausage and cook for an additional 5 minutes until the sausage is heated through and browned slightly.
In a large mixing bowl, combine the cooked rice, sautéed sausage and vegetable mixture, shrimp, fire-roasted tomatoes, Cajun seasoning, salt, and pepper. Stir until everything is well combined and evenly distributed.
Pour the mixture into a greased 9x13 inch baking dish. Spread it out evenly so that it cooks uniformly.
In a small bowl, combine the grated parmesan cheese, plain bread crumbs, salt, and pepper. Sprinkle this mixture evenly over the top of the casserole. This will give your dish a deliciously crunchy topping.
Cover the baking dish with aluminum foil and place it in the preheated oven. Bake for 25 minutes, then remove the foil and bake for an additional 10-15 minutes, or until the top is golden and crispy.
Once baked, remove the casserole from the oven and let it sit for a few minutes before serving. This Louisiana Casserole is best enjoyed hot, perhaps with a sprinkle of fresh parsley for garnish. Serve it alongside a fresh green salad or some crusty bread for a complete meal.