Preheat oven to 220 C.
Place beetroot in a shallow roasting dish and the onions, pears and fennel (if using) in a separate dish. Whisk the olive oil, vinegar and sugar together and pour evenly over the two pans. Mix through.
Spread the items in the dish to a single layer and bake for 40 - 50 mins, stirring a couple of times during baking. Liquid should be mostly evaporated and beetroot tender.
Bake walnuts (if using) in a separate dish for approximately 12-15 minutes.
Allow to cool and dress salad greens with an extra splash of olive oil and balsamic vinegar.
Add roasted items topped with walnuts or salad toppers and mix gently with your fingers. Crumble feta over salad and eat while still warm. Enjoy!