Peel and quarter the potatoes, then cook in a large pan of salted, boiling water for 15 mins. Drain and set aside.
Pour a glug of olive oil into a large frying pan over a medium heat and cook the sausages for 15 mins. Add the tomatoes to the pan for the final 5 mins. Mash the potatoes well and mix in the pesto. Season and serve with the sausages and tomatoes.