For the mayo: Add the mayonnaise, parsley, lemon juice, lemon zest and some salt and pepper to a bowl, and mix by hand until combined.
For the clams casino: In a saute pan over medium-low heat, add the olive oil, garlic, shallots and some salt. Sweat the aromatics for 5 minutes. Add the pickling liquid and wine, and bring to a simmer. Add the clams and cover until the clams open, 5 minutes.
Remove the clams and set aside. Take the meat out of the shells, chop them and toss back into the sauce with the butter and 1/4 cup of the breadcrumbs to tighten up the mixture, adding more to thicken, if needed. Add some black pepper and reduce the cooking liquid slightly.
Add the bacon to a saute pan and cook until the fat is rendered and the bacon is crispy. Remove to a paper-towel-lined plate and crumble. Reserve 2 tablespoons of the bacon grease in the pan. Add the remaining 1/2 cup panko into the same saute pan and toast over medium-low heat until the breadcrumbs are crispy and lightly browned.
For the sandwich build: On a slice of baguette, spread some of the lemon parsley mayo and pile a generous amount of the clams casino mixture on top. Garnish with crumbled bacon, toasted panko, cherry pepper slices and parsley leaves before serving.