After roasting veggies, let them cool completely. Transfer veggies to a zip-top freezer bag in a single layer. Freeze up to 2 months. When ready to use, thaw in the fridge 12 hours or overnight. Spread them out on a tray. Drizzle with olive oil. Reheat in oven at 375°F. Do not microwave roasted veggies or the generated steam will make them soggy.