In a large non-stick pot, add olive oil and diced onions. Cook the onions until carmelized. Add the diced bell peppers, and then add the beef and toss often to brown all sides of the beef cubes. Meanwhile, boil some water and pour in a separate bowl with the tomatoes and pasilla peppers. Let stand for about 10-15 minutes. Peel the tomatoes (the peels should come off very easily after soaking in the hot water). Slice the pasillas open, remove the seeds & stems, and chop (roughly). Take 2 of the tomatoes and place in a blender with the chopped pasillas and blend - - this will make a mole-like paste. Add to the pot. Blend the remaining tomatoes and add to the pot, stirring frequently. Add-in the cocoa powder, Ortega chili peppers and corn. Let the mixture cook on simmer for about 90 minutes.
Then remove the beef cubes and add-in the black beans. Pull the beef cubes apart (shred) with 2 forks and this will give you a nice pile of shredded beef. If the beef is thoroughly cooked, then it should be tender enough to do this pretty easily). Once done shredding, add the beef back into the pot and stir-in the spices. Cook for an additional 30 minutes. Enjoy!