Preheat the oven to 250 degrees.
Line a baking tray with parchment or a silicone mat for easy cleanup. Set aside.
Combine the brown sugar, honey, oil, vanilla, salt, and cocoa powder to a large bowl. Whisk to fully combine, making sure no clumps remain.
Add the oats and nuts, if using. Toss to fully combine.
Spread the mixture onto the prepared tray, spreading into an even layer.
Bake for 30 minutes.
Gently mix, trying not to break up any clusters, and bake an additional 30 minutes.
Turn off the oven and allow the granola to cool completely inside.
Keep stored in an airtight container until ready to enjoy.