Preheat the oven to 190C/gas 5. Rub raw beetroots with olive oil and wrap them in one piece of foil. Roast the beetroot until fork tender. The cooking time will vary according to the size of the beetroot, but will probably be around 1 h- 1h1/2 when cooked. Leave to cool.
Cook the pasta in boiling water as per instructions.
Peel the skin, remaining stems or hard bits off the beetroots and cut into small bite-sized chunks.
Fry the garlic in a pan with a few glugs of olive oil for a couple of minutes over a medium heat. Add the beetroot and saute for a further few minutes to ensure it's hot.
Crumble the block of feta cheese into the pan, stirring until all is melted in. Add a little of the pasta water to make the sauce a bit thinner.
Spoon the creamy beetroot mixture over the drained pasta and toasted walnuts and fresh herbs.