Place the tofu, chives, mayonnaise, and mustard in a bowl and mix well. Season with pepper. Set aside.
Combine the tomato and hummus in a separate bowl until the tomato is coated. Season with pepper, set aside.
Combine the sour cream, horseradish, and lemon juice in a third bowl. Set aside.
To assemble the sandwich, carefully slice the bread lengthwise with a very sharp knife into 4 long slices of equal thickness. Place the first slice on a serving platter and cover with the tofu filling. Cover with a second slice of bread. Spread with the hummus-tomato filling. Cover with a third piece of bread. Spread with the sour cream mixture and cover with overlapping slices of cucumber. Top with the last slice of bread.
Place the drained cottage cheese in a food processor fitted with a metal blade. Process until very smooth and creamy. Spread over the top and on the long sides of the sandwich stack, leaving the two ends unfrosted.
Make a lattice with chives by criss-crossing them on top of the sandwich cake. Decorate the sides with cucumber slices, tomato skin roses, fresh herbs, and edible flowers. Refrigerate until ready to serve. When ready to serve, cut a thin slice off the unfrosted ends to expose the fillings. Cut the remaining sandwich cake into 3/4-inch-thick slices.