Season Salmon generously with Salt and Pepper on both sides.
Arrange one Salmon fillet and 1/4 of the Asparagus in the center of one 12x12 inch piece of foil.
Repeat with the remaining Salmon and Asparagus on 3 other pieces of foil.
Slide lemon slices under the Salmon and Asparagus.
In a small bowl, mix Butter, Italian Seasoning, and Garlic.
Drop large dollops of the herb butter on top of the Salmon and Asparagus.
Fold the foil tightly around the Salmon and Asparagus, being sure to seal the ends together tightly so the juices and butter doesn't run out while cooking.
Grill over medium-high heat for 6-8 minutes on each side, OR bake at 400 F for 20 minutes, until Asparagus is tender and Salmon is flaky.
Drizzle fresh lemon juice over the top and serve immediately.