For a Nicoise Salad, you can really use any greens you prefer or have on hand. The recipe calls for a container of mixed greens, which typically include a variety of lettuces like romaine, oak leaf, lollo rosso, and tender leafy greens such as spinach or chard. However, feel free to customize it to your liking. Arugula can add a peppery bite, while butter lettuce will lend a soft, buttery texture.