Preheat the oven to 200C.
In a clean bowl, mix the sweet potato with the olive oil, garlic, and Cajun seasoning. Lie on a baking tray lined with parchment paper and roast for 12-15 minutes until the potatoes are tender and begin to brown. Set aside and leave to cool.
To make the dressing, mix all the ingredients together in a bowl and season to taste. Transfer to a screw-top bottle and set aside.
In a clean bowl, toss the cooled sweet potatoes together with the other salad ingredients. Dress with 2 Tbsp of the chive and buttermilk dressing. Store the remainder in the fridge for up to 3 days.
Season to taste and spoon into serving dishes.