Slice the spaghetti squash in half vertically and scoop out the seeds. Drizzle each half with a tablespoon of olive oil and half a teaspoon of salt.
Preheat the Air Fryer to 400°F / 205°C. Add the spaghetti squash halves face up, working in batches if necessary, cook for 25-27 Minutes, until lightly browned and steaming. Remove from the air fryer basket and repeat if necessary.
Meanwhile, in a large mixing bowl, whisk together the milk, cream, remaining salt, and cornstarch until smooth and no lumps remain. Add all the cheese, grated garlic, and lemon zest and stir to combine. Divide evenly among the two spaghetti squash halves.
Air fry at 400°F / 205°C for 10-12 Minutes, until the cheese is bubbling and browned on top. Serve warm!