Directions

1. Preheat oven to 375°F. Bring a large pot of water to a boil over high heat. Add noodles; cook, stirring occasionally, until slightly softened but still somewhat firm, about 5 minutes (the noodles will be undercooked). Add asparagus; cook, stirring often, until the asparagus is bright green and tender-crisp and the noodles are fully cooked, about 2 minutes. Drain and set aside.
2. Wipe the pot clean. Add 2 tablespoons oil and heat over medium-high heat. Add leek; cook, stirring occasionally, until softened and translucent, about 5 minutes. Add garlic; cook, stirring often, until fragrant, about 1 minute. Sprinkle with flour. Reduce heat to medium and cook, stirring constantly, for 2 minutes. Gradually add milk, whisking until smooth. Bring to a gentle boil over medium-high heat, whisking often. Reduce heat to medium-low; gently simmer, whisking often, until thickened, about 5 minutes. Remove from heat. Add mustard, salt, pepper and cayenne; stir until well combined. Add the noodle-asparagus mixture, salmon and peas; fold until the noodles are fully coated. Spread the mixture evenly in a 2-quart baking dish.
3. Combine panko, cheese, parsley and the remaining 1 teaspoon oil in a medium bowl; stir until well mixed. Sprinkle evenly over the casserole. Bake until the cheese is melted and the topping is golden brown, about 15 minutes. Let stand for 5 minutes before serving.