Peel and wash the vegetables. Cut into medium pieces: potatoes into large cubes, carrots into rounds and onions into slices.
Place them in a deeper oven dish, pour over about 50 ml of oil, add spices - be careful, don't put much salt, it will harden the potatoes and they will take longer to cook.
Mix well with your hands or a spoon, to coat the veggies well with oil and spices.