Preheat the oven to 300 degrees and cover a large baking sheet with parchment paper.
In a large bowl, stir together the oats, almonds, walnuts, chia seeds, and flax seeds. Set aside.
Combine the honey, peanut butter, and vanilla in bowl and microwave 30 seconds, or until the ingredients can easily be mixed. Stir until incorporated.
Pour the wet mixture into the dry ingredients and mix until evenly coated.
Spread the mixture in a thin layer on the prepared baking sheet. Bake for about 15-20 minutes, stirring halfway through. Let cool completely before breaking apart.