Make just enough of this recipe. Use the portion planning tool to calculate exactly how much of each ingredient you’ll need.Place potatoes in a pot of salted boiling water and cook until just soft, remove and cool.Preheat grill for high heat, brush the tuna with oil and season with salt and pepper and grill for a couple of minutes on each side. Let rest before slicing.Make the dressing and set aside. Place the spinach, tomatoes, olives and potatoes in a bowl toss with a small amount of the dressing. On 1 serving plate, top with sliced tuna and a drizzle of the dressing.