In a large bowl, whisk the mustard with the red wine vinegar. Slowly whisk in the olive oil and season with salt and pepper. Add half of the spinach and toss with the hot lentils and red onion until the spinach has wilted. Season the salad with salt and pepper and let stand for 10 minutes. Just before serving, toss the salad with salami, olives, basil and the remaining spinach. Serve warm or at room temperature.