Heat 1 tbsp of oil in a frying pan over medium heat, and sauté onion for 5 minutes. Add in the chilli and garlic, then continue for another 1 minute. Transfer to a bowl, and leave to cool for 5 minutes.
Next, add the turkey mince, half the mint, half the lemon zest and 1 tbsp of dry couscous into the bowl. Season with salt and pepper, mix well and shape into 16 meatballs. Pop them in the freezer for 15 minutes.
In the meantime, put the remaining couscous in a bowl with the remaining lemon zest. Pour over the hot stock, cover and set aside for 15 minutes.
Blanche the peas in a pot for 2 minutes. Drain and set aside.
Make the sauce by mixing the yoghurt, minced garlic, the remaining mint and half the lemon juice. Season with salt and pepper then set aside.
Fluff up the couscous with a fork, and mix in the remaining lemon juice, peas, and sliced radishes. Season to taste.
Heat the remaining 1 tbsp of oil in a frying pan over medium heat. Fry the meatballs for 10 minutes, turning regularly until browned all over. Cover with a lid and cook for 5 more minutes on low heat, until thoroughly cooked.
Serve turkey meatballs with the couscous salad and yoghurt.