Put the potatoes in a large pan and cover with cold water. Bring to the boil and cook for 12-15 minutes until tender. Drain and lightly crush with a fork, then stir in 1 tablespoon of the oil. Set aside and keep warm.
Heat a frying pan over a medium heat and add the halved tomatoes. Cook for 2 minutes, until they start to soften. Stir the tomatoes into the warm potatoes, along with the parsley, lemon zest and olives. Season with black pepper. Put the pesto and lemon juice in a bowl and mix together.
Drizzle the beef escalopes with the remaining oil and season with black pepper. Put the frying pan back over a high heat and sear the beef quickly for about 1 minute on each side. Slice in half and serve with the potato mixture with a little pesto dressing drizzled over.