Preheat oven to 225°. Grease a large baking sheet with cooking spray. Slice zucchini into very thin rounds, using a mandolin if you have one! Pat zucchini with paper towels to draw out excess moisture.
In a large bowl, toss zucchini with oil then toss in ranch seasoning, oregano, salt, and pepper. Place in a single layer on baking sheets. Bake until crispy, about 1 hour 20 minutes, checking after about an hour. Let cool to room temperature before serving.
Recipe by 5* trending recipes with videos at https://food.theffeed.com/2019/05/02/cool-ranch-zucchini-chips/