Arrange a rack in the middle of the oven and heat to 325°F (163℃). Line an 8x8-inch baking pan with parchment paper that hangs over the pan on 2 sides to form a sling. Coat the pan and a large bowl with cooking spray.
Place the nuts in a single layer on a rimmed baking sheet. Toast until lightly browned and fragrant, 8 to 10 minutes. Coarsely chop the toasted nuts while still warm. Transfer to the greased bowl.
Add the chopped prunes, puffed rice, flaxseed meal, sesame seeds, chia seeds, and vanilla. Stir with a silicone spatula to combine.
Warm the brown rice syrup in a microwave-safe bowl for 30 seconds to make it easier to pour.
Immediately pour the warm syrup over the nut mixture and stir until the nuts and seeds are evenly coated.
Transfer the nut mixture to baking pan. Scrape the nut mixture into the prepared pan. Press into an even and compact layer with the spatula. Sprinkle the salt over the top.
Bake the bars. Bake until the bars are dry and lightly toasted, 18 to 20 minutes.
Partially cool the bars in the pan. Place the pan on a cooling rack and cool the bars in the pan until they are pliable and can be lifted out of the pan with the parchment sling without breaking apart, 20 to 30 minutes.
Lift the slab out of the pan and place on a cutting board. Spray a large knife with cooking spray and cut the slab into bars. Do not move the bars once they have been cut, leave them on the cutting board to cool completely.
Once the bars have cooled and set, combine the chocolate and coconut oil in a shallow, wide, microwave-safe bowl, such as a cereal bowl. Microwave on high power until melted, 30 to 60 seconds, stirring halfway through.
Place a sheet of parchment paper on a work surface. Dip the bottom of each bar in the chocolate and place on parchment. Refrigerate the bars for about 15 minutes to set the chocolate.
Transfer the bars to an airtight container, dividing each layer with a piece of parchment to keep the bars from sticking together. Bars can also be wrapped individually in parchment paper for easy transport.