Spoon 1/4 cup of the San Marzano sauce onto a plate. Place an eggplant slice on top. Add a layer of goat cheese mushrooms. Top with another eggplant slice, then a layer of caramelized onions, then another eggplant slice. Spread 1/8 cup of San Marzano sauce on top of that, put another eggplant slice on top, and then top with some caramelized onions, and a bit of basil.