Bring water to a boil in a big pot.
Wash the potatoes.
Add potatoes and salt to the pot and let it boil on low heat until almost soft but still not ready to eat (this will vary depending on the potato size and variety, 15-20 min).
Preheat the oven or air fryer to 220 degrees Celsius.
Drain the potatoes and place on a parchment covered baking sheet if baking in the oven, or on a cutting board if making them in the air fryer.
Gently press down on the potatoes using a fork, glass or potato masher until they are a bit flattened.
Drizzle with a little bit of olive oil and sprinkle with sea salt. Place the baking sheet in the oven and bake for approximately 15 minutes or 10-12 minutes in the air fryer, until soft, golden brown and crispy.
Place the potatoes together with some arugula in a bowl.
Drizzle with pesto all over, grate the cheese and top with chopped pistachio nuts.