Preheat the oven to 400°F (210°C).
Wash and remove the skin from the potatoes (if you want to).Insert each potato into your spiralizer using a medium size blade and start turning to create spiral-shaped potato strips. Repeat this process with all your potatoes. With a kitchen towel or paper towels, remove any excess moisture from the potatoes by pressing them and squeezing them gently.
Peel and thinly slice the red onion. If you have a spiralizer that can handle onions, you can also spiralize it.
Spread the potato and onion noodles on a parchment-lined baking sheet and drizzle with extra-virgin olive oil.
Sprinkle with salt, pepper, chili flakes, dried oregano, and freshly chopped rosemary.
Toss to coat with your fingers, and then place the noodles in the oven.
After 15 minutes, if any bits start to brown too quickly, cover them with aluminum foil. Continue to bake the spiralized potatoes until they crisp up, checking every couple of minutes. After 30 minutes, all noodles should be cooked and ready to eat.
Let the spiralized potatoes cool for 5 minutes to crisp up a bit more, and then serve immediately.