Turn the Ninja pressure cooker to Saute mode and heat the cooking oil.
Add the chopped onions and sauté for 2-3 minutes, until softened.
Stir in the garlic and cook briefly until fragrant.
Add the ground beef and cook until browned, breaking it up with a wooden spoon or spatula.
Add the bell pepper then mix to combine.
Season with cumin, coriander, oregano, thyme, paprika, chili powder, cayenne, salt, and pepper. Stir to combine.
Mix in the kidney beans, beef stock, and dark chocolate (optional).
Pour in the diced tomatoes, tomato paste, (do not stir) to prevent a burn notice.
Close the lid, set the valve to Seal, and cook on High Pressure for 15 minutes.
Allow pressure to release naturally for 10 minutes, then do a quick release for any remaining pressure.
Open the lid, stir well, and let the chili rest for a few minutes before serving.