Make the burger sauce: In a bowl, mix vegan mayo, mustard, ketchup, pickle juice, diced pickles, sugar, salt, pepper, garlic powder, onion powder, and paprika. Set aside.
Make the filling: Drain and mash the black beans. Mix with the vegan ground beef, salt, pepper, and garlic powder until well combined.
Add to tortillas: Spread a thin, even layer of the filling over one side of each tortilla, pressing it down firmly.
Cook: Heat a little avocado oil in a medium skillet over medium heat. Place the tacos filling-side down and cook until the filling is golden and crispy.
Flip & add cheese: Flip the tacos and place vegan cheddar on top. Cook until the tortilla is golden and the cheese is melted.
Add toppings: Top with shredded lettuce, sliced onion, and pickles.
Drizzle with sauce: Finish with a generous drizzle of homemade Big Mac burger sauce and serve hot!