Cook potatoes - place potatoes in a pot of cold water, and bring to the boil. Boil 20 minutes, or until potatoes are tender. You know they are cooked when you can stick a knife in them and the knife goes straight through. Combine harissa spice, olive oil, salt and pepper and lemon juice in a small bowl and whisk until combined. Once potatoes are cooked, drain water and roughly chop potatoes in half. Add harissa mix and spring onions/green onions to potatoes and stir. In a large salad bowl, lay out arugula/rocket. Top with potato mix and toss. Add fetta, mint and sprinkle over pine nuts. Adjust salt and pepper to taste.