I have a dilemma I could use some advice for. I am looking for a way to roast veggies at relatively high heat (maybe 425 degrees) without using oil. Any ideas? I know you're not supposed to use nonstick surfaces at high heat, but not sure how high exactly. Right now I slather olive oil onto aluminum foil over regular baking sheets, and it works fine -- just trying to see if there's a way to do it sans added fat...?