Line a 7×5 pan with parchment paper (or double the recipe for an 8×8), and set aside. Gently warm the peanut butter until it reaches an easily spreadable consistency. Stir together with the sweetener and salt (and oil, if using), then add in the quick oats and stir until evenly mixed. Scoop the batter into the prepared pan, spread out, then put a second sheet of parchment over the top and press down firmly. Press down with a spatula or roll a can over the top to really press it in. Freeze 1/2 an hour or until firm, or refrigerate 2-3 hours or until firm. Cut into slices with a sharp knife. I store these in the fridge or freezer.