Make the Thousand Island-inspired dressing. In a small bowl, stir together the vegan mayonnaise, sweet onion, chopped pickles, ketchup, lemon juice, paprika, salt, and pepper. Set aside.
Make the sandwich. Lay your tomato slices out on the cutting board and season them with salt and pepper. Let them sit for a few minutes.
Lay 2 slices of bread out so that each side of the sandwich is like an opened book. On one side, spread a couple tablespoons of the Thousand Island-inspired dressing. On the other piece of bread, spread the yellow mustard.
Place one butter/Boston lettuce leaf on each piece of bread. Use more than one leaf if you really want to cover the whole piece of bread. I like a ton of lettuce in a sandwich, so I layer up!
On the piece of bread with the Thousand Island-inspired dressing, lay down the seasoned tomatoes on top of the lettuce. Then, layer the sweet onion and strips of pepperoncini pepper on top. Place the sauerkraut in an even layer on top of that.
Now, take one handful of bean sprouts and evenly arrange them over the sauerkraut. I like to arrange these in the opposite direction of how I'll be cutting the sandwich so that they're lined up all nice (as you can see in the photos). Then, take a handful of broccoli or alfalfa sprouts and press them on top. These sprouts tangle up and make a nice “mass” that kind of keeps everything together/unified.
From here, the piece of bread with the mustard and butter/Boston lettuce and place it on top. Repeat these steps for the second sandwich. Cut each sandwich in half and enjoy!