Preheat the oven to 425℉.
If the salmon is not already cut into portions, slice it into four 4-ounce fillets, leaving the skin intact.
Spray a large 13 x 9 inch baking dish with non-stick cooking spray. Place salmon fillets into it, skin-side down, with a little space between each one.
Whisk together the butter, garlic, dill, salt, and pepper in a small bowl. Drizzle equal amounts of the butter sauce over all of the fillets and place one lemon slice on each one.
Cover the baking dish with a piece of aluminum foil and bake in the preheated oven for 12-15 minutes. Remove the aluminum foil during the last 2-3 minutes of cooking to allow the edges to crisp up slightly.
Serve salmon immediately with additional fresh dill and lemon juice, if desired.
