Preheat the oven to 250 F. Line baking sheets with parchment paper. Spray with non-stick cooking spray or just brush some oil on the parchement paper
Slice the zucchini as thin as you possibly can. Use mandolin slicer if you have one. Place in a large bowl, drizzle with some oil and season lightly with some salt and toss to mix everything. Arrange the zucchini slices on the baking sheets and pop into the oven and roast for about 1 hour or longer (it takes longer on my oven). They should be lightly golden and crispy at the end of baking. Check on them during baking time. You may need to remove some that are already golden brown and crispy.