In a small bowl, stir together the chili powder, cumin and ½ teaspoon each salt and pepper. In a medium bowl, combine the beef, 1 tablespoon of the spice mixture and ¼ cup plus 2 tablespoons water. Using your hands, mix well; set aside.

In a large bowl, using a potato masher, mash half of the beans to a coarse paste. Add the tomatoes with juices and mash until they are broken down. Stir in the remaining whole beans; set aside.

In a large Dutch oven over medium, heat the oil until shimmering. Add the onion and ½ teaspoon salt; cover and cook, stirring occasionally, until the onion begins to soften and brown, about 7 minutes. Add the tomato paste and cook, stirring often, until well browned, 2 to 3 minutes. Add the remaining spice mixture and cook, stirring, until fragrant, about 30 seconds.

Add 2 cups water and bring to a simmer over medium-high, scraping up any browned bits. Add the meat mixture and cook, breaking it into small bits, until the meat is no longer pink, about 1 minute. Add the bean-tomato mixture and cocoa, then return to a simmer. Reduce to medium and simmer gently, uncovered and stirring occasionally, until the chili has thickened, about 30 minutes. Off heat, taste and season with salt and pepper. Serve with finely chopped onion for sprinkling.