Scrub the new potatoes and slice in half. Tip into a pan and cover with cold water and sprinkle in a good pinch of salt. Bring to the boil, then reduce the heat to a simmer for 15-20 mins, till they’re tender and are pieced easily with the tip of a knife.
Peel and finely slice the red onion, and slide into a bowl. Grate in the lemon zest and squeeze over the juice. Peel and grate in the garlic clove. Sprinkle in a little salt and pepper and toss everything together. Set aside to lightly pickle while you complete the rest of the dish.
Scatter the samphire into a sturdy bowl and cover with boiling water. Allow to sit for 1 min, then drain and cover with cold water. Drain again and shake dry, then tip into a large bowl. Slice the cherry tomatoes in half and add to the samphire.
Drain the cooked potatoes and add to the large bowl. Tip in the onions and their lemony liquid. Drizzle in 1 tbsp oil and toss together well. Finish with a scattering of rocket leaves. Spoon the seashore salad onto plates and serve.