Peel the potatoes and slice them into thin, even rounds (about 1/8 inch thick). Slice the zucchini into thin rounds as well, leaving the skin on. As for the onion, you can either slice it thinly or dice it into small cubes, depending on your preference. Set everything aside, ready to cook.

Heat the olive oil in a nonstick skillet (about 8 to 10 inches wide) over medium heat. Once hot, add the sliced potatoes. Cook them gently for about 10–12 minutes, stirring occasionally, until they are soft but not browned. If you'd like to use an air fryer instead, toss the potatoes with a teaspoon of oil and cook them at 375°F (190°C) for about 15 minutes, shaking halfway through.

In the same pan or a separate one, add a bit more oil if needed and sauté the onion and zucchini over medium heat for 5–7 minutes, until they are soft and lightly golden. Remove all the cooked vegetables from the pan and let them cool slightly.

In a large mixing bowl, crack the eggs and whisk them until smooth. Add the salt and stir again. Once the vegetables have cooled a bit, add them to the eggs and mix until everything is well combined.

Wipe the skillet clean and heat it again over medium heat. Pour the egg and vegetable mixture into the pan and spread it out evenly. Cover with a lid and cook on medium-low heat for about 8–10 minutes, until the edges are set and the top is mostly cooked but slightly moist.

To flip the tortilla, place a large flat plate or lid over the skillet, hold it firmly, and flip the pan so the tortilla lands on the plate. Then, carefully slide it back into the skillet to cook the other side. Continue cooking for another 5–6 minutes, uncovered, until fully cooked through.

Let the tortilla rest for a few minutes before slicing into wedges. Serve warm or at room temperature.