1.Roasting the Vegetables. Prepare medium-hot coals.
2. Place the beetroots and butternut directly into the coals and cook, turning occasionally, until tender, about 25–30 minutes.
3. Remove from the heat and brush off most of the charred skins.
4. Chop 3 beetroots into quarters and scoop out bite-size chunks of butternut from the skins.
5. Puréeing the Beetroot. Place 3 roasted beetroots into a food processor with olive oil and vinegar. Purée until smooth, then season to taste.
6. Preparing the Dressing and Walnuts. Blitz the dressing ingredients in a blender until smooth and season.
7. Dry-toast the nuts in a pan and chop roughly.
8. Assembling the Salad. Spread the beetroot purée on the serving dish.
9. Top with lettuce, roasted beetroot quarters and butternut, avocado and slices of red onion.
10. Pour the dressing over the salad and sprinkle with toasted walnuts.