Preheat the oven to 220C/425F/Gas 7.
For the chicken, cut a pocket down the side of the beast using a sharp knife and stuff with the Brie and basil, then season, with sea salt and freshly ground black pepper.
Heat the oil in an ovenproof frying pan over a high heat. Place the chicken breast in the pan and cook for two minutes, on each side, until golden brown.
Place the frying pan into the oven and roast for 15-20 minutes, or until completely cooked through.
For the sweet potato, place the cooked potato, oil and butter into a bowl and mash, then fold in the cashew nuts.
To serve, toss the mangetout with the oil in a bowl and place on a serving plate. Place the chicken breast and mashed potato onto the plate. Garnish with a few basil leaves.