In a medium pot, sauté the onions, peppers and garlic in a drizzle of oil over medium-high heat. Add the black beans, red kidney beans and chickpeas, the tomatoes and tomato paste, chili powder, cocoa, chipotle chili en adobo and cumin. Bring to a simmer, reduce heat and cook for an hour, or until thickened. Cool and refrigerate for up to a week or freeze for up to 6 months, then reheat the whole pot or individual servings. Top with a blop of sour cream.