Tossing veggies with olive oil, salt and pepper then throwing them in a 200C oven is often the go-to way to roast them, but lowering the temperature results in perfectly roasted veggies you won't be able to stop eating. Image from katerha.
By roasting your vegetables at 120C, you can cook larger pieces (like whole carrots or half a head of cauliflower) more easily, and there's no risk of burning the outside while undercooking the inside. Amiel Stanek, writing at Bon Appetit, explains what you get instead:
We mean dry roasting that veg with a little olive oil, a good sprinkle of salt, and a sprinkle of chile flakes for good measure -- in a 250° [Fahrenheit] degree oven until the exterior gets all shrivel-y and the interior takes on a delicate, custard-like texture. This is less about adding brash browned notes than it is concentrating natural flavours, yielding vegetables that taste distinctly and deliciously of themselves.
Besides being incredibly tasty on their own, vegetables cooked this way are great for purees or soups since they add creaminess without a burnt flavour.
Stop Roasting Your Veg in a Screaming-Hot Oven [Bon Appetit]