Step 1: Prepare the Shrimp

• If your shrimp are raw, bring a large pot of salted water to a boil. Add the shrimp and cook for 2-3 minutes, or until pink and opaque. Drain immediately and set aside to cool.
• Pat the shrimp dry with paper towels and chop into bite-sized pieces if desired.

Step 2: Cook the Vegetables

• Preheat your oven to 350°F (175°C). Grease a 9×13-inch casserole dish or a similar baking dish with butter or nonstick spray.
• In a large skillet, melt 1 tablespoon of butter over medium heat. Add the chopped onion, garlic, and bell peppers. Sauté for 3-4 minutes, or until the vegetables are tender and fragrant.
• Stir in the frozen peas (or green beans) and cook for another 2 minutes. Remove from heat.

Step 3: Make the Creamy Sauce

• In a medium saucepan, melt 3 tablespoons of butter over medium heat. Add the flour and whisk continuously for 1-2 minutes to form a smooth roux.
• Gradually pour in the milk, whisking constantly to prevent lumps. Cook for 3-5 minutes, or until the sauce thickens and coats the back of a spoon.
• Stir in the Parmesan cheese, ½ cup of the cheddar cheese, paprika, thyme, salt, and black pepper. Mix until the cheese is melted and the sauce is smooth.

Step 4: Assemble the Casserole

• In a large mixing bowl, combine the cooked rice, sautéed vegetables, shrimp, and creamy sauce. Mix well to coat everything evenly.
• Transfer the mixture to the prepared casserole dish, spreading it into an even layer. Sprinkle the remaining ½ cup of cheddar cheese on top.

Step 5: Add the Topping

• In a small bowl, mix the breadcrumbs with the melted butter. Sprinkle the breadcrumb mixture evenly over the top of the casserole.

Step 6: Bake

• Bake the casserole in the preheated oven for 25-30 minutes, or until the top is golden brown and bubbling.
• Let the casserole rest for 5-10 minutes before serving. Garnish with chopped parsley, if desired.