Step 1

Preheat oven to 425 degrees. In a large pot of boiling salted water, cook pasta 2 minutes less than package instructions (it will be undercooked). Drain. In a small bowl, toss together panko, Parmesan, and 2 teaspoons oil.

Step 2

In pot, heat 2 tablespoons oil over medium-high. Add onion, season with salt and pepper, and cook until softened, 8 minutes. Add flour and whisk to coat onion with flour. Slowly whisk in broth, then milk.

Step 3

Cook, stirring constantly, until sauce comes to a boil. Reduce heat and simmer, stirring frequently, until sauce is thickened, about 8 minutes. Stir in pasta, tuna, and peas and season to taste with salt and pepper.

Step 4

Transfer tuna mixture to a 9-by-13-inch baking dish and top with panko mixture. Bake until sauce is bubbling and crust is golden, 17 to 20 minutes. Let cool 10 minutes before serving.