Heat your oven to 200°C/Fan 180°C/Gas 6. Peel the sweet potatoes and cut each into five or six wedges. Put in a roasting tin and toss with 1 tbsp of olive oil. Season with salt and pepper. Roast for 15 mins.
While the potatoes roast, squeeze the juice from half the lime into a bowl or dish. Mix in 1 tbsp Cajun seasoning then add the chicken breasts. Turn to coat and set aside to marinate while the sweet potatoes are roasting.
After the potatoes have cooked for 15 mins, add the chicken and their marinating juices to the roasting tin, nestling them among the sweet potatoes. Roast for 25 more mins till the chicken is golden and cooked through.
Meanwhile, squeeze the remaining lime half into a large bowl. Finely dice the tomatoes and add to the lime. Peel and finely chop the onion. Add that too.
Halve the chilli. Scoop out the seeds and white bits for less heat. Finely chop it. Add to the tomatoes. Give everything a good mix. Pick the coriander leaves from the stalks and add these to the bowl. This is your pico de gallo.
Divide the cooked chicken between two warm plates and spoon over the pico de gallo mixture. Serve with the sweet potato wedges and any tangy juices from the pan.