Preheat your oven to 350°F (175°C) and line a 9x13-inch baking pan with parchment paper.
In a large mixing bowl, cream together the room-temperature butter, white sugar, and brown sugar until the mixture is light and fluffy.
Beat in the eggs one at a time, followed by the vanilla extract.
Mix in the 1/2 cup of creamy peanut butter until the batter is smooth and well combined.
In a separate bowl, whisk together the baking soda, salt, all-purpose flour, and old-fashioned rolled oats.
Gradually add the dry ingredients to the wet ingredients, stirring until you have a uniform dough.
Press the dough evenly into the prepared 9x13-inch pan.
Bake in the preheated oven for about 20-25 minutes, or until the bars turn golden brown.
If desired, melt the peanut butter and the chopped dark chocolate in two separate microwave-safe bowl in 20-second intervals, stirring in between until smooth. Drizzle them each over the baked bars.
Allow the bars to cool in the pan for about 10 minutes, then cut them into long rectangles for easy on-the-go snacks.
Pack them into your bento box and take them along on your bike rides for a delicious and energizing snack.