Preheat your oven to 375 degrees Fahrenheit. This step is crucial as it ensures that your casserole cooks evenly and thoroughly.
Grab a 9×13-inch baking dish and give it a quick spray with non-stick cooking spray. This will help your casserole come out easily once it's done.
In a large skillet, heat ¼ cup butter over medium-high heat until melted. You want it to look bubbly and fragrant, filling your kitchen with delicious aromas.
Add ½ yellow onion and the diced 1 red bell pepper and 1 green bell pepper to the skillet. Sauté these vegetables until they become tender, which should take about 5-7 minutes. Look for them to turn translucent and soften.
Now, stir in 2 cloves garlic and let it cook for an additional minute. You’ll know it’s ready when you can smell the garlic wafting through the air.
Next, add 14 ounces andouille sausage to the skillet, stirring well to combine. Allow this to cook for about 5 minutes until the sausage starts to brown slightly. This will deepen the flavors.
Incorporate the 1 pound shrimp into the mixture, seasoning it with 1 teaspoon salt and ½ teaspoon pepper. Cook until the shrimp turns pink and opaque, which should take about 3-5 minutes. You want to be careful not to overcook them!
Once the shrimp is ready, transfer the entire skillet mixture into your prepared baking dish. This vibrant mixture of shrimp, sausage, and vegetables looks inviting already!
Add 3 cups cooked rice and the 1 (14.5-ounce) can fire-roasted tomatoes to the baking dish. Don’t forget those 2 tablespoons Cajun seasoning! Stir everything together well, ensuring the rice is distributed evenly throughout.
In a separate small bowl, mix together ½ cup parmesan cheese, ⅓ cup plain bread crumbs, ½ teaspoon salt, and ½ teaspoon pepper. This will form a delightful topping.
Sprinkle the breadcrumb mixture over the casserole, creating a lovely crust that will turn golden brown in the oven.
Place the baking dish into your preheated oven and bake for 20 minutes. You’re looking for the topping to be golden and crispy.
Once it's done, remove the casserole from the oven and let it rest for a few minutes before serving. This resting time helps all the flavors meld together.