I put lots of olive oil on the roast before the glaze so that some of it, with the glaze, runs onto the onions underneath. This causes the onions to caramelize and they're delicious to eat.
I also add powdered garlic to the glaze and sprinkle dried rosemary on top of glaze which adds to the flavour.
And when sliced (hot or cold the next day) I spread mint jelly on mine although other family members turn their noses up at this one.