Sprinkle salmon with 1/4 teaspoon salt and pepper. Using long-handled tongs, moisten a paper towel with cooking oil and lightly coat the grill rack. Grill salmon, covered, over medium heat or broil 4-6 in. from the heat for 12-18 minutes or until fish flakes easily with a fork.
Meanwhile, cook pasta according to package directions. In a large skillet, saute asparagus and leeks in oil with until asparagus is crisp-tender. Sprinkle with remaining salt and pepper.
In a small bowl, combine the cornstarch, water, broth, dill and lemon juice until smooth; stir into asparagus mixture. Bring to a boil; cook and stir until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Drain pasta; toss with asparagus mixture. Serve with salmon.