Baked salmon in foil with asparagus and lemon garlic butter sauce

Preheat the oven to 375°F (190°C).
Cut four sheets of aluminum foil, about 12 inches long.
In a small bowl, mix together melted butter, minced garlic, lemon juice, lemon zest, salt, and pepper.
Place one salmon fillet in the center of each sheet of foil.
Brush each salmon fillet generously with the butter mixture.
Divide the asparagus evenly among the four foil packets, placing the asparagus around the salmon fillets.
Drizzle the remaining butter mixture over the asparagus.