Prep the air fryer: Preheat to 380°F (193°C) for 3–5 minutes.
Lightly brush or spray the basket with 1/2 tbsp olive oil to reduce sticking.
Mix aromatics: In a large bowl, combine the grated onion, garlic, lemon zest, lemon juice, 1 1/2 tbsp olive oil, egg, salt, and pepper. Whisk with a fork.
Build the mixture: Add ground chicken, breadcrumbs, dill, parsley, and oregano. If using, fold in feta or sun-dried tomatoes.
Mix gently with a spatula or your hands until just combined. Don’t overwork; it can make the meatballs tough.
Shape: Lightly oil your hands. Scoop about 2 tablespoons per meatball and roll into 1 1/4–1 1/2-inch balls. You should get 16–18 meatballs.
Arrange and cook: Place meatballs in a single layer in the air fryer basket, leaving a little space between each.
Air fry for 9–12 minutes, shaking the basket or turning meatballs halfway.
Check doneness: The meatballs should be lightly browned and reach an internal temperature of 165°F (74°C). If needed, cook 1–2 minutes more.
Rest and serve: Let them rest 2–3 minutes to set the juices. Serve with tzatziki, pita, and a quick chopped salad of tomatoes, cucumbers, red onion, and olives.