Heat the oil in a large saucepan over medium-high heat. Cook the beef, turning, for 5 mins or until brown all over. Transfer to a plate.
Add the capsicum and onion to the pan and cook, stirring, for 5 mins or until softened. Add the garlic, cumin, coriander, paprika and cayenne pepper and cook, stirring, for 1 min or until fragrant.
Return the beef to the pan. Add the stock and tomato and bring to the boil. Reduce heat to low. Simmer, covered, for 1½ hours or until beef is tender. Use tongs to transfer the beef to a bowl, then use two forks to coarsely shred.
Return the beef to the pan. Add the beans and vinegar. Simmer, uncovered, for 10 mins or until thickened slightly. Stir in the chopped coriander.
Meanwhile, heat the tortillas in the microwave following packet directions.
Place the beef mixture in a serving bowl. Sprinkle with coriander leaves. Serve with tortillas, sour cream and steamed brown rice, if desired.