Heat olive oil in a large frypan over medium heat. Add onion, celery, carrot, green capsicum and garlic: saute until tender. Stir in tomatoes, chilli powder, tomato paste, vinegar and pepper. Cover, reduce heat then simmer 10 minutes.
Stir in kidney beans then cook an additional 5 minutes.
Cut a 1/2cm slice off the top of each bread roll; set aside. Hollow out the centre of each roll, leaving about 1/2cm thick shells; reserve the inside of rolls for other uses.
Spoon bean mixture evenly into rolls and replace tops. Serve immediately.