Toss the meat in the seasoned flour. Heat the olive oil and butter together in a frypan over a medium heat and brown the meat all over to seal it.
Place the onions, carrots, celery and garlic in the bottom of the slow cooker and lay the browned meat on top. Pour the tinned tomatoes over the meat then pour over the stock. Add the bay leaf and oregano.
Cook for 8 hours on Low setting or 4 hours on High and a couple more on Low.