Cook the Noodles: Bring a large pot of salted water to a boil. Add the egg noodles and cook until just tender according to package directions, usually 7-9 minutes. Drain thoroughly and set aside.
Prepare the Flavor Base: Preheat your oven to 400°F (200°C). In a large Dutch oven over medium heat, melt the butter. Add the minced garlic and diced shallots, cooking gently while stirring until they release a fragrant aroma and soften, about 2 minutes.
Create the Sauce Roux: Sprinkle the flour over the softened shallots and garlic, stirring constantly to coat and cook the flour for about a minute, until it turns slightly golden.
Build the Creamy Sauce: Slowly whisk in the half-and-half and the Dijon mustard, stirring frequently to avoid lumps. Let the mixture simmer gently until it thickens slightly, about 4-5 minutes.
Add Cheese and Combine: Remove the Dutch oven from heat. Stir in the shredded cheddar until melted and smooth, creating a rich, creamy sauce.
Mix in Main Ingredients: Fold the cooked noodles, drained tuna, and green peas into the cheese sauce. Season generously with salt and freshly ground black pepper to taste.
Prepare the Crispy Topping: In a small bowl, combine Panko breadcrumbs, grated Parmesan, lemon zest, and olive oil. Mix well until the crumbs are evenly coated.
Assemble and Bake: Sprinkle the Panko topping evenly over the casserole mixture in the Dutch oven. Transfer to the oven and bake until the topping is golden brown and the casserole is bubbling, about 25-30 minutes.
Garnish and Serve: Remove from oven and let cool slightly. Garnish with fresh chopped chives before serving for a fresh, herbaceous finish.
