Step 1: Preheat your oven to 400°F (200°C). Prepare four sheets of heavy-duty aluminum foil, approximately 12x12 inches each.
Step 2: In a small bowl, whisk together the melted butter, minced garlic, and chopped parsley to create the sauce for the baked salmon in foil with asparagus and garlic butter sauce.
Step 3: Place a salmon fillet in the center of each foil sheet and divide the asparagus evenly among the four packets, placing it alongside the fish.
Step 4: Season the salmon and asparagus with salt and pepper, then drizzle the garlic butter sauce generously over each portion.
Step 5: Place two lemon slices on top of each salmon fillet. Fold the foil over the salmon and asparagus, sealing the edges tightly to create a packet.
Step 6: Place the packets on a large baking sheet and bake for 15-20 minutes, depending on the thickness of the salmon.
Step 7: Carefully open the packets (watch out for steam!) and serve the baked salmon in foil with asparagus and garlic butter sauce immediately.