How to Make It
Heat the olive oil in a large pot. Add the onion and bell pepper and cook, stirring occasionally, over moderately high heat until the onions are soft and translucent, about 5 to 7 minutes. Add the jalapeño and garlic and cook for 1 minute. Add the chili powder, cumin, cocoa, oregano, paprika, cayenne, red pepper, salt and a few turns of black pepper; cook, stirring, until fragrant, 1 to 2 minutes.
Stir in the tomatoes and the chicken broth and bring to a boil. Reduce to a simmer, add the chicken breast and cook for 20 minutes, stirring occasionally. Transfer the chicken to a cutting board and use two forks to pull it. Return it to the soup. Stir in the corn, if using.