Preheat the oven to 200 degrees C. Arrange the eggplant, sweet potatoes, parsnips and leeks in a single layer in a wide roasting tin. Use a pastry brush to coat them lightly with oil.
Sprinkle the thyme over the vegetables and season with freshly ground black pepper. Bake for 25–30 minutes until the vegetables are almost tender, then turn the vegetables and add the pear wedges, turning to coat lightly in oil. Arrange the bacon rashers over the vegetables.
Return the tin to the oven for 15–20 minutes until the vegetables and pears are tender and the bacon is lightly browned. Drizzle the balsamic vinegar over the roast vegetables and serve hot.