New potatoes don’t need peeling, just gently scrub with a soft brush or sponge, and rinse to remove any dirt. Dice the potatoes in half. Put the potatoes into a pan of lightly salted water enough to cover the potatoes. Bring the water to a boil and simmer until tender, about 15-20 minutes, (depending on size). Rinse under cold water and drain. Set aside. Cut the green beans in half. Place the green beans in a steamer basket in a pan with 1-inch of water. Steam for 4-5 minutes until tender. Rinse under cold water, drain and place the potatoes and green beans in a large bowl.
Grate the lemon on the small edge of a box grater. To make the dressing, add the extra virgin olive oil, garlic-infused oil, lemon zest, red wine vinegar, Dijon mustard, a pinch of salt, and a good grind of black pepper to a small bowl. Whisk to combine.
Place the eggs into a pan of cold water, enough to just cover the tops. Set the pan over medium heat. Once the water starts to boil, set the timer for 6 minutes. Rinse under cold water to stop them from cooking further. Use a small teaspoon to peel the shell away from the egg. Cut the eggs into quarters. Set aside.
Finely dice the green ends of the scallions and discard the white ends. Finely dice the celery, cucumber and chives. Add the scallions, celery, cucumber, and chives to the potatoes and green beans. Dice the baby gem lettuce, flake the mackerel, drop in the black olives and the diced eggs to the bowl.
Drizzle the dressing over the salad. Toss to coat everything with the dressing. For best results leave to chill in the fridge for a couple of hours before serving.