Place beetroot and garlic into a large, lined roasting tray/dish. Drizzle with oil and toss well to coat. Sprinkle with salt and pepper and place into the oven to roast for 25 minutes.
Add onion to dish and roast for another 10 minutes.
Add walnuts to dish and roast for another 10 minutes.
Remove roasting tray from oven and allow to cool.
Pop roast veg, walnuts, dried herbs, tahini and lemon juice into a blender or food processor. Blend on low-speed, increasing to high-speed, until desired consistency is achieved.
Transfer dip to a serving dish, garnish with fresh coriander leaves, and serve.