Place the cubed root vegetables (all cubed to a similar size) in a large roasting tin. Drizzle with olive oil and sprinkle with oregano, salt and pepper. Toss to coat. Spread the veg across the roasting tin evenly in one layer, being careful not to overcrowd the tin (otherwise the veg will steam instead of roast!).
Roast the vegetables in the preheated oven till tender and slightly caramelised, about 15 to 20 minutes. Remove from oven and either serve immediately tossed with crumbled feta and chopped parsley, or set aside to cool slightly before assembling the salad and serving.
Since beetroot and parsnip can turn quite sweet after roasting, I sometimes use a regular potato instead of a sweet potato to cut down on the sweetness of the salad. The salad is also good with a drizzle of balsamic vinegar to finish.