Preheat the oven to 275°F (135°C). Line a sheet pan with parchment paper and set it aside.
In a large bowl, combine the oats, seeds, nuts, millet, cocoa powder, and salt.
In a small bowl, whisk together the avocado oil, maple syrup, and vanilla extract.
Pour the wet ingredients over the dry mixture and stir well until everything is evenly coated.
Spread the mixture in a thin, even layer on the prepared sheet pan. Bake for 30 minutes without stirring. Start checking the granola at the 30-minute mark and continue checking every 5 minutes until it smells toasted and looks as golden brown as it can (chocolate makes it kind of hard to tell!). Be careful that it doesn’t burn!
Remove the granola from the oven and let it cool completely on the baking sheet without stirring. Once cool, stir in the dark chocolate chips or chunks.
Transfer to an airtight container. Store at room temperature for up to 5 days or freeze for longer storage.