Crush rice chex cereal in a large bowl using your hands until only small pieces remain. It’s okay if a few larger pieces remain but you want the bulk of it to be small pieces.
Add oats to the bowl with crushed rice chex and stir to combine.
Prepare peanut butter by mixing PB2 with water in a small bowl until creamy (skip this step if using normal peanut butter).
Combine applesauce, vanilla, honey and peanut butter in a medium saucepan. Cook over low heat until ingredients are melted together and creamy/gooey, about 5-10 minutes.
Pour warm gooey applesauce mixture from step 4 over the chex oat mixture and stir until dry ingredients are completely intertwined with wet ingredients (well combined).
Line a 9×9 baking dish with parchment paper. Pour mixture from step 5 into the dish and smooth out using a spatula until mixture completely fills the dish. Sprinkle brown sugar over the top then push it into the bars using your fingertips. Refrigerate for about 5 hours to allow granola bars to harden.
Once hardened, remove from fridge, slice into 16 bars and enjoy!