Preheat oven to 350 degrees. On a rimmed baking sheet, line heavy duty tin foil with enough overlapping to make a pouch. Lay lemon slices down, then top with salmon. Place pats of butter on top, then season with salt and pepper. Lift foil up and fold tightly to make a nice little cooking bag. Bake for 25 minutes, or until cooked to your liking. Enjoy!