When the turkey is mostly cooked, add the cumin, oregano, chili powder, and cornmeal and cook, stirring constantly, until the mixture is aromatic, about 3 minutes. Add the chicken broth, tomatoes, and cocoa powder. Stir until the mixture simmers and the cocoa dissolves. Stir in the beans and cover the pot. Transfer to the oven and cook until the meat is very soft and the flavors are very fragrant, 4 to 8 hours.