Preheat your oven to 350°F (175°C) and line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal.
In a large mixing bowl, combine the rolled oats, almond flour, salt, and cinnamon. Stir until well mixed.
In a separate bowl, whisk together the honey (or maple syrup), melted coconut oil, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until fully combined. Fold in the mixed berries and chopped nuts if using.
Transfer the mixture to the prepared baking dish and press it down firmly into an even layer.
Bake in the preheated oven for 25-30 minutes, or until the edges are golden brown.
Allow the bars to cool in the baking dish for about 10 minutes, then lift them out using the parchment paper and let them cool completely on a wire rack before cutting into squares.