Place tomatoes, peppers, carrots, celery, onion, and garlic in your food processor and chop very finely. (If you do not have a food processor, you will have to chop all the vegetables yourself.)
Roll the lamb shanks in the flour and shake off the excess flour.
Heat the olive oil in a large saucepan and fry the shanks until nicely browned.
Place the shanks in an oven tray of your choice.
Add the finely chopped vegetables, red wine, bay leaves, oregano, and stock to the shanks. Season with salt and freshly ground black pepper and cover with foil or lid
Place in the preheated oven and cook for 20 minutes then lower heat to 160° C/ 320° F
Cook for at least 3 hours or until the meat virtually falls off the bone. Uncover the meat and let it cook further to reduce some of the juice if necessary.