Mix peanut butter, rice syrup, and vanilla and heat over a low heat in a small sauce pan until the mixture becomes warm and syrup (this will only take a few minutes).
While your peanut butter syrup is heating, spray a large bowl with cooking spray before adding the rice cereal. Pour ooey gooey peanut butter syrup over the cereal and combine until all of the rice cereal is evenly coated.
Transfer brown rice into an 88-baking dish that has been lightly coated with non-stick cooking spray. Pat them down and make them nice and even, pop in the fridge about an hour or so, then cut em up and enjoy!