Preheat the oven to 375°F (190°C). Line a rimmed baking sheet with a sheet of foil, placing the salmon skin-side down with the long side of the fillet parallel to the long side of the pan; fold the foil edges up about 2 inches to contain juices.
Tuck the thin lemon slices under and around the salmon so they are evenly spaced beneath the fillet; set aside.
In a microwave-safe bowl or small saucepan, melt the butter. Stir in the lemon juice, honey, and minced garlic until combined.
Pour or spoon about three-quarters of the butter mixture evenly over the salmon, reserving the remainder to finish after baking. Season the top of the salmon with the kosher salt and black pepper.
Seal the foil over the salmon, adding a second sheet of foil on top if needed, and crimp the edges to make a mostly airtight packet. If desired, let the salmon marinate in the packet for 10–15 minutes for more flavor.
Place the foil packet on the prepared baking sheet and bake at 375°F for about 17 minutes, or until the salmon is nearly cooked through.
Carefully remove the baking sheet from the oven and open the top of the foil so the salmon is exposed while keeping the foil edges raised to hold juices.
Set the oven to high broil. Spoon the reserved butter mixture over the salmon if there is not an excessive amount of pan juices.
Broil the salmon for 5–10 minutes, watching closely, until the top is as golden as you like and the salmon reaches your preferred doneness.
Remove from the oven, garnish with chopped parsley if using, and serve immediately.