Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub the potatoes in cold water. Chop them into bite-sized pieces.
Trim and peel the parsnips and carrots. Chop into chunky fingers. Peel the red onion. Slice into wedges through the root.
Tumble the potatoes, parsnips, carrots and red onion into the roasting tin. Toss with a glug of olive oil. Season with salt and pepper.
Nestle the chicken thighs in amongst the vegetables. Sprinkle a little salt over the skin.
Pop in the oven and roast for 45 mins till the chicken is cooked through with crisp golden skin, and the vegetables are tender. Give the veg a stir halfway through the cooking time so they brown evenly.
Rinse the parsley. Pat dry. Pick the leaves off the stalks and chop roughly.
Take the tin out of the oven. Scatter the parsley over the chicken and veg. Serve straight away.