Heat the oven to 200 C Gas 6. Cut the tomatoes in half and arrange in a baking tray. Season with salt and pepper, drizzle with 1 tbsp olive oil and bake for 20 minutes.
Cook the potatoes and beans in simmering salted water until tender. Drain and cut the potatoes in half. Peel the hard boiled eggs and cut into quarters.
Heat 1 tbsp olive oil in a non stick frying pan and sear the tuna steaks for 3 minutes on each side, leaving the inside pink.
To make the dressing whisk the vinegar, olive oil and mustard in a large bowl with sea salt and pepper until thick.
Dress the rocket leaves, potatoes, beans and olives and arrange on dinner plates with the tomatoes and eggs, Cut the tuna into chunks and place on top with the anchovy fillets. Serve immediately.