PREP: Line an 8x8-inch pan with parchment paper or foil, adding an overhang for easy removal. Don't spray with cooking spray as it makes these bars greasy. Set aside.
DATES: See Note 1. In a small blender jar (I use the small Twister jar and Blendtec) or a food processor, pulse the pitted dates to create a very thick and sticky paste. This can takes some patience; stir with a spoon and re-blend as needed.
ADD NUT BUTTER: Scoop out every last bit of the date paste and add to a large bowl. Add in the peanut butter, maple syrup, and vanilla extract. Use an electric hand mixer to beat until combined.
REMAINING INGREDIENTS: Stir in the quick oats, old-fashioned oats, miniature chocolate chips, and coarsely chopped pistachios. (If the pistachios and peanut butter you are using aren't salted, add a scant 1/4 teaspoon salt here, too.) Mix until thoroughly combined. If needed, knead the mixture with your hands to get a well-combined and incorporated mixture.
FORM INTO BARS: Transfer the mixture into the prepared 8x8-inch baking pan and very firmly press the mixture into an even layer. Use the bottom of a flat 1 cup measuring cup to help firmly press. Set aside.
OPTIONAL CHOCOLATE TOPPING: In a large, microwave-safe bowl, combine the chocolate chips and coconut oil (measured when the oil is in a hardened state). Microwave in bursts of 15 seconds, stirring in between each burst for 15 seconds, until melted and smooth. Pour melted chocolate evenly over the bars, and tip the pan around to create an even layer of chocolate on top. Cover and refrigerate until the chocolate is completely set.
CUT INTO BARS: Using the parchment paper overhang, remove the bars from the pan and cut into equal-sized bars. Store leftover bars in the fridge, covered, for up to 1 week.