Pre-heat the oven to 170°C/gas 3. Mix together 2 tsp of the oil and 1 tsp of the vinegar. Lightly brush over the turkey steaks and season with freshly ground pepper. Set aside to marinate while you make the braised red cabbage.
Heat 3 tsp of the oil in a flameproof casserole 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, apple slices, orange zest and juice, remaining vinegar and sugar to the casserole. Lightly season, then stir the ingredients together.
Cover the casserole with a tight-fitting lid and cook in the oven for 1½ hours or until the cabbage is just tender, stirring halfway through the. Towards the end of the, pat the marinated turkey steaks dry on kitchen paper.
Heat a cast-iron, ridged griddle or heavy frying pan and brush with the remaining oil. Add the turkey steaks and cook on one side only over a moderately high heat for about 1½ minutes until browned. (The steaks will still be undercooked at this stage.)
Stir the lentils into the red cabbage, then place the steaks on top, browned-side up. 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 turkey cooked through. Serve at once.
Pork steaks are also delicious cooked this way. Pan-fry 4 well-trimmed pork (shoulder) steaks for 2 minutes on each side until golden brown. Substitute barely ripe pears for the apples and braise the pork on top of them.