Preheat oven to 225 degrees Fahrenheit. Line two large baking sheets (I used two 17" baking sheets) with silicon baking mats or parchment paper. Slice your zucchini on a mandolin. Mine had 1, 2, or 3 for thickness and I used 2.
After you slice your zucchini, place the slices on a sheet of paper towels and take another paper towel and sandwich the zucchini slices and press on them. This helps draw out the liquid so it'll cook a bit faster.
Line up the zucchini slices on the prepared baking sheet tightly next to each other in a straight line, making sure not to overlap them.
In a small bowl, pour your olive oil in and take a pastry brush to brush the olive oil on each zucchini slice.
Sprinkle salt throughout the baking sheet. Do NOT over-season, in fact, it's better to use less salt initially because the slices will shrink; so, if you over-season, it'll be way too salty! You can always add more later.
Bake for 2+ hours until they start to brown and aren't soggy and are crisp.
Let cool before removing and serving. Keep in an airtight container for no more than 3 days.