Roasted Potato and Asparagus Lentil Salad with Tangy Mustard-Lemon Dressing Vegan, gluten-free, grain-free, nut-free, refined sugar-free, soy-free ★ ★ ★ ★ ★ The dressing makes a lot - 2/3 cup - so I prefer to stir in half of the dressing into the salad and then serve the rest of the dressing on the side to drizzle on top. After the potatoes have roasted for 15 minutes, flip the potatoes and return them to the oven along with the asparagus (and red onion if you are roasting that) for another 12-15 minutes.