Make the Patties: Combine dry ingredients, add water, soy sauce, and marmite. Mix well and let rest for 30 minutes.
Prep Toppings: Make burger sauce, slice tomatoes, shred lettuce, dice onions, and prepare pickles. Slice off the outer crust from an extra bottom bun to create the middle bun layer.
Form Patties: Form the mixture into 4 patties.
Cook Patties: Fry patties in a non-stick pan over low heat for 15 minutes, flipping halfway. Add vegan cheese and a few drops of water to melt.
Assemble: Layer the ingredients on the buns in the classic Big Mac order: bun, sauce, lettuce, patty with cheese, onions, middle bun, sauce, pickles, lettuce, tomatoes, patty with cheese, onions, sauce, top bun.
Serve: Serve immediately and enjoy!