Put the pork steaks into a shallow non-metallic dish. Put the cornflour and soy sauce in a small bowl and mix to a smooth paste, then add the ginger, garlic, black bean sauce and a little pepper. Pour over the pork, cover with clingfilm and marinate in the refrigerator overnight.
Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the pork and marinade into the slow cooker pot. Pour over the boiling stock, cover with the lid and cook on high for 30 minutes. Reduce the heat and cook on low for 7½–9½ hours, or set to auto for 8–10 hours, until the pork is cooked through and tender.
When almost ready to serve, heat the oil in a large frying pan, add the mixed vegetables and stir-fry for 2–3 minutes or until just tender. Spoon the pork on to plates lined with rice and top with the vegetables.