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, beet 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 1 1⁄2 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.