Preheat the oven to 200°C, fan oven 180°C, gas mark 6.
Put all the vegetables into a roasting tin and add the olive oil, tossing to coat. Roast for 20 minutes, then turn the vegetables over, adding the cumin seeds (if being used). Roast for another 15 minutes, until tender.
You could use butternut squash as an alternative to sweet potatoes.
While the vegetables are roasting, prepare the dips. Put the ingredients for the beetroot dip into a blender and blend for 15-20 seconds until smooth. For the cucumber dip, mix the cucumber and yoghurt together. Keep covered and chilled until ready to serve.
You can serve the vegetables cold for a tasty nibble.