In a small bowl, mix vegan mayo, vinegar, mustard, ketchup, smoked paprika, onion powder, garlic powder, turmeric, and salt until combined.
Notes
Many copycat Big Mac sauce recipes don't call for ketchup since it is not listed in their ingredients list, however, I find that it provides a little sweetness, makes it taste like the authentic sauce, and makes the color look more authentic too. You can also swap out the ketchup with a little sugar instead.
When using this for a salad dressing, I double the amount of white vinegar to thin it out a little and give it a bit more tang.