Preheat the oven to 400 degrees F. Lay a large piece of aluminum foil over a baking sheet with enough overhang to make a foil packet that will completely cover the salmon. Set aside.
In a small bowl, whisk together the melted butter, garlic, brown sugar, salt, and pepper until combined.
Cut the salmon into 4 even portions. Lay the salmon on the foil, leaving a bit of space between each piece. (see note) Spoon the butter mixture over each filet, spreading it evenly over the surface.
Lay the lemon slices on top of the salmon and tightly wrap the tinfoil around the fish, crimping the edges together to make sure there are no gaps.
Bake for 12-15 minutes, or until the salmon is cooked through and flakes easily with a fork.
Remove from the oven, sprinkle some chopped parsley on top, and plate with your favorite sides. Serve warm.
Notes
You can cut the salmon into four 6-ounce portions or six 4-ounce portions.
If you're using skin-on salmon, spray the foil with some non-stick cooking spray. If using skin-on, place the salmon skin side down. The skin will stick to the foil, and you can use a spatula to separate the meat from the skin easily.