heat a drizzle of oil in a large, preferably nonstick, pan over medium-high heat. add carrot and season with salt and pepper. cook, stirring, until just tender, 3-4 minutes. transfer to a medium bowl. add zucchini and another drizzle of oil to pan. cook, stirring, until tender, 5-6 minutes. season with salt and pepper. transfer to bowl with carrot. add mushrooms and another drizzle of oil to pan. cook, stirring, until tender, 3-5 minutes. season with salt and pepper. turn off heat; transfer to same bowl. wipe out pan.