Step 1: Cook the Pasta

1. Bring a large pot of salted water to a boil. Add the pasta and cook until al dente, following the package instructions (usually 1-2 minutes less than fully cooked since the pasta will continue cooking in the oven).
2. Drain the pasta and set it aside.

Step 2: Prepare the Creamy Sauce

1. In a large saucepan, melt the butter over medium heat. Once melted, add the flour and whisk continuously for 1-2 minutes to form a roux. The mixture should turn light golden and smell slightly nutty.
2. Gradually pour in the milk, whisking constantly to avoid lumps. Add the chicken or vegetable broth (if using) and continue whisking until the sauce thickens, about 3-5 minutes.
3. Stir in the garlic powder, onion powder, Dijon mustard, salt, pepper, paprika, and nutmeg. Taste and adjust the seasoning as needed.
4. Once the sauce is smooth and thickened, remove it from the heat and stir in ½ cup of shredded cheddar cheese and ¼ cup of grated Parmesan. Mix until the cheese is fully melted and incorporated.

Step 3: Assemble the Pasta Bake

1. Preheat your oven to 375°F (190°C).
2. In a large mixing bowl, combine the cooked pasta, drained tuna, frozen peas (if using), and the prepared creamy sauce. Gently stir until everything is evenly coated.
3. Transfer the mixture to a greased 9×13-inch (or similar-sized) baking dish. Spread it out evenly with a spatula.
4. Sprinkle the remaining ½ cup of shredded cheddar cheese and ¼ cup of Parmesan cheese over the top for a cheesy, golden crust.

Step 4: Bake

1. Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the cheese is melted, bubbly, and slightly golden.
2. If you prefer a crispier topping, switch to broil mode for the last 2-3 minutes. Keep a close eye to prevent burning.

Step 5: Serve

1. Remove the pasta bake from the oven and let it rest for 5 minutes before serving.
2. Garnish with chopped parsley (optional) and serve warm.