Preheat the oven to 300°F and line two large baking sheets with parchment paper.
Using a mandoline slicer, slice all of the vegetables as thinly as possible, ideally 1/16 inch thick. If you don’t have a mandoline you can use a knife, however, be sure to slice them as thinly as possible – this is the only way to ensure they get crispy.
Once sliced, place the beets on a cutting board lined with a paper towel, season generously with salt and allow them to sit for 10 minutes to help pull out any water. Once complete, pat the sliced beets dry to help remove any excess moisture. (This step is not necessary for the sweet potatoes and parsnips as they have lower water content.)
In a large bowl, add the sliced vegetables, drizzle with olive and toss until all slices are well coated. (I like to do the red beets separately so their colour does not bleed onto the other vegetables.)
Once the vegetables are coated in oil, place them on to the parchment paper-lined baking sheet, be careful to not overlap them. (You may need to cook them in batches if you can’t fit all of the vegetable slices on the baking sheets.)
Transfer the baking sheets to the oven to bake for 20 minutes. After 20 minutes, remove from the oven, flip the sliced vegetables and then return to the oven, rotating the pan, and allow to bake for an additional 15 minutes. The vegetables should be pretty crispy at this point, if not, leave them in the oven for 5 minutes increments, checking on them to ensure they do not burn until they are crispy and the edges are golden.
Once baked, remove the pans from the oven and season the veggie chips generously with salt and allow to cool completely on the pan.
Once cooled, serve immediately. If needed, the veggie chips can be stored in an airtight container for several hours or up to 1 day, left any longer they will begin to lose their crispiness.