Place pork, in single layer, in large baking dish, bake, uncovered, in very hot oven about 25 minutes or until pork is browned and cooked as desired. Cover; stand 5 minutes before slicing thickly.
Meanwhile, heat half of the stock in medium frying pan, cook leek and garlic, stirring, until leek softens and browns slightly. Add sugar and vinegar; cook, stirring, about 5 minutes or until leek caramelises. Add remaining stock; bring to a boil. Reduce heat; simmer, uncovered,about 5 minutes or until liquid reduced by half. Place leek mixture in medium bowl; cover to keep warm.
Peel, core and halve apples; cut into thick slices.
Melt butter in same pan; cook apple and extra sugar, stirring, until apple is browned and tender.
Boil, steam or microwave carrot, squash and asparagus, separately, until just tender; drain.
Serve pork, topped with caramelised apple and sweet and sour leek, on top of the mixed vegetables.