In a large skillet over medium heat, brown ground beef in batches, draining any excess fat before putting it into the bottom of the slow cooker. While you are doing this, chop onions and peppers; set aside.
Once all the beef is browned, drained and in the slow cooker, heat olive oil in a large pan and add the vegetables.
Sauté the vegetables over medium heat until the volume in the pan starts to reduce and the onions become translucent.
Add herbs and seasonings to the pan; cook until fragrant and the volume continues to decrease in the pan. There should be little to no moisture in the base of the pan.
Drain diced tomatoes and add those to the pan, stirring the mixture thoroughly before adding to the slow cooker. No need to stir; just layer the vegetable mixture on top and pat down.
Add the beef stock to the slow cooker before putting on the lid and turning on the slow cooker. Cook for two hours on high heat.
Mix arrowroot powder with a bit of water to make a paste, then add to chili as a thickener. Add cocoa powder and stir until well combined. Season to taste with salt, then cook for another hour on high.