Grease and line a 9-inch square pan with parchment paper.
Place oats in a large mixing bowl. Add cinnamon and salt and mix to combine.
Finely chop mix-ins by hand or blitz in the food processor.
Pour the mix-ins into the bowl of oats.
In a small bowl, combine the honey, peanut butter, an vanilla extract. If needed, warm the peanut butter slightly to make it more stirrable. Be sure the mixture has returned to room temperature before mixing in any chocolate.
Pour the liquid ingredients into the dry ingredients. Mix the two together.
Transfer the granola mixture to the prepared pan. Use a wooden spoon to distribute the mixture evenly, then use the bottom of a flat sturdy object (like a drinking glass), to firmly pack the mixture down in an even layer.
Cover and refrigerate for at least one hour, or up to overnight, giving the oats time to absorb some of the moisture.
Remove the bar from the pan, and use a sharp knife to slice the bars into 16 pieces. Wrap bars individually in plastic wrap or parchment paper to store.