When you're already using the oven to cook a main dish, take advantage of the oven being on. For best results, it's recommended to cook the vegetables separately for some time and then place the roast on top of the veggies later on. Make sure to cut them into uniform sizes to ensure even cooking. You can use a variety of vegetables such as carrots, potatoes, bell peppers, and onions. Toss them in olive oil, salt, pepper, and any herbs or spices of your choice for added flavor.