It's probably not a great selling point that it takes 5 days to make this sandwich. But making your own sprouts is worth it. Once you have sprouts, the rest comes together easily: a quick pickle of the cucumber and carrots with seasoned rice wine vinegar, a spicy Russian dressing and then mindful layering and stacking of ingredients for the ultimate vegetarian sandwich.
Use a sharp vegetable peeler to make long slices of the cucumber, turning when you encounter the seeds. Peel the carrot and then make long slices of carrot. Put the cucumber slices and carrot slices in a shallow bowl and add the rice wine vinegar. Let them marinate while you prepare the dressing and other sandwich components.
To make the spicy Russian dressing, combine the mayonnaise, relish, ketchup and sriracha in a small bowl until well blended. Taste for seasoning and set it aside.
To assemble the sandwiches, place 2 slices of the bread on a cutting board and spread thickly with the avocado from edge to edge. Layer over the avocado with by folds of the carrot slices followed by folds of the cucumber slices to make a thick and even layer as in the photos. (You may have some leftover slices.) Arrange the tomato in an even layer on the top.
Top the vegetables with the sprouts. Spread the remaining 2 slices of bread with the spicy Russian dressing and top the sandwiches with them. Use a very sharp bread knife and a gentle sawing motion to slice them in half, if desired. Or, serve them whole and have plenty of napkins on hand.