Boil, steam or microwave potatoes until tender, set aside to cool.
Heat a large frying pan, spray with oil. Add onion and garlic, cook over low heat for 5 minutes, or until softened. Add chicken, cook for 2 minutes or until heated through.
In a medium jug, whisk light evaporated milk and cornflour until smooth, whisk in pesto. Add mixture to frying pan; bring to boil; reduce heat and simmer 2 minutes or until sauce has thickened slightly. Transfer to a large serving bowl; toss through potatoes, tomatoes and rocket.
