Preheat the oven to 170°C. Mix together 2 teaspoons of the oil and 1 teaspoon of the vinegar. Lightly brush over the pork and season. Set aside to marinate.
Heat 3 teaspoons of the oil in a flameproof casserole dish with a capacity of at least 3 litres. Add the onion and fry gently for 3 minutes. Add the garlic, cook for a few seconds, then remove from the heat. Add the cabbage, beetroot wedges, pear slices, orange zest and juice, remaining vinegar and sugar to the casserole. Lightly season, then stir the ingredients together. Cover the dish with a tight-fitting lid and cook in the oven for 1½ hours or until the cabbage is just tender, stirring halfway through the cooking time. Towards the end of the cooking time, pat the marinated pork steaks dry on paper towel.
Heat a heavy-based frying pan and brush with the remaining oil. Add the pork steaks and cook for 2 minutes on each side over a medium–high heat until browned. (The steaks will still be undercooked at this stage.)
Stir the lentils into the red cabbage mixture, then place the steaks on top. Blend together the stock and mustard and drizzle over the top. Re-cover and return to the oven for 15–20 minutes until the cabbage is tender and the pork cooked through. Serve at once.