Bake the potatoes - Slice the potatoes in half, drizzle with a little oil, salt, and pepper, and bake at 190°C for 30 minutes until golden and tender.
Cook the eggs - Add the eggs to boiling water and cook for 6 minutes. Transfer to cold water to stop the cooking, leave to cool, then peel, slice in half, and set aside.
Prep the green beans - Top and tail the beans, then boil for 5 minutes. Drain and place into cold water to keep them bright and crisp.
Cook the chicken - Slice each chicken breast in half horizontally to make four thin pieces. Drizzle with oil, salt, and pepper, then cook on a hot griddle pan until charred and cooked through. Slice once rested. Make the dressing - Whisk together the olive oil, vinegar, and Dijon mustard until emulsified into a thick, glossy dressing. Assemble the salad - Start with the salad leaves, then add the potatoes, green beans, eggs, tomatoes, olives, and sliced chicken. Drizzle with the dressing and serve.