Prepare Onion: Grate one large brown onion using a grater or food processor. Place grated onion in a bowl with a strainer on top to collect juice. Squeeze out as much excess onion juice as possible to help the kebabs stick together.
Make Marinade: In a separate bowl, combine 1 tsp salt, 1/2 tsp red sumac, 1/4 tsp black pepper, 1/4 tsp ground turmeric, and 1/4 tsp baking soda. Mix well.
Mix Meat and Onion: Add the squeezed grated onion to 500g lamb mince (80% meat, 20% fat). Add the marinade mixture to the meat and onion. Mix thoroughly until the mixture comes together into a soft ball.
Chill Mixture: Cover the meat mixture with plastic wrap and refrigerate for a couple of hours, ideally not overnight, to allow flavors to meld.
Shape Kebabs: Add warm water to the reserved onion juice to help shape the kebabs. Lightly oil the air fryer basket. Take about half a handful of the meat mixture and shape into flat sausage shapes using the warm water to help. Place shaped kebabs in the air fryer basket.
Air Fry Kebabs: Preheat air fryer to 200°C (392°F). Cook the kebabs for 12 minutes total, flipping halfway through after 6 minutes to ensure even cooking.
Serve: Remove kebabs from air fryer. Brush with melted butter. Serve garnished with fresh mint, radish, onion, and alongside grilled tomato and grilled chili.