Drain the oil from 1 tin of sardines into a small bowl and set aside. Drain the oil from the second tin into another small bowl and mix it with 1 tablespoon of parsley, vinegar, lemon zest, and black pepper. Add the sardines and stir. Let sit for a bit so the flavors marry. Toast your bread in a normal toaster or, if you want to be all Alton-style fancy, heat the oven to the broiler setting on high and place oiled-swiped bread (using the remaining sardine oil) on the rack. Only keep them in there for 2 to 3 minutes, otherwise they will go from golden brown and crisp to charred and sad. Halve the avocado and remove the pit. Smoosh the flesh in each half with a fork. Spread this green goodness evenly onto the toasted bread, then top with a nice scoop of the sardine mixture. Pour any remaining sardine oil dressing on top and garnish with the remaining parsley. Season with sea salt and a nice big squeeze from the lemon wedges.