Combine all the kafta ingredients in a bowl, season well with salt and pepper and mix thoroughly.
Using your hands, shape the beef mixture into balls about the size of golf balls. Thread each ball onto a metal or soaked wooden skewer and squash into a sausage shape. Refrigerate until needed.
To make the dipping sauce, combine the yogurt with the harissa paste, lemon juice and zest and season to taste with salt and pepper. Add more lemon juice if needed.
Brush oil on the kaftas and grill on a hot fire or griddle pan, turning occasionally until cooked through and brown on all sides, about 6 minutes. Heat up the naan bread alongside the kaftas.
Dip the kaftas in the spicy yoghurt sauce and serve with lemon wedges and the warmed naan bread.