Place the chicken breasts on a baking tray, drizzle with oil, season and roast in the oven for 20 minutes, until cooked through.
Meanwhile, put the quinoa in a saucepan and cover with 3 times its volume of cold water. Bring to the boil, then simmer for about 6-8 minutes until just tender.
Drain and rinse the quinoa and tip it into a mixing bowl. Add the celery, lemon juice, rapeseed oil and salt and pepper and mix together.
Make the pesto by blitzing all of the ingredients in a food processor until it forms a rough paste.
Cut each peach in half around the stone, pull the 2 halves apart and slice each half into bite-sized wedges.
Once the chicken is cooked, cut it into strips and serve with the quinoa salad, peaches and pesto.