How to make meatball style food that keeps its shape
Overworking the meat is generally what you want to avoid for a burger, but in the case of kebab meat it may help. It will give it a denser and bouncier texture.

To do this, when mixing in the other ingredients, just mix for a bit longer than you normally would, especially with your hands as the heat will probably melt the fat slightly and help to bind it. Keep working it until the texture is smooth.