Yes, but I don't recommend adding any vinaigrette to the salad until you're ready to eat it. Feel free to assemble the salads and cover them with plastic wrap and keep them in the fridge about a day. When you're ready to serve the salad, then drizzle it with vinaigrette and enjoy immediately. Remember though, if the salad is prepped ahead, apple will start to turn brown from oxidation, and spinach and onion will start to wilt.