Whisk together mayonnaise, cream cheese, lemon juice, Dijon mustard, parsley, horseradish, Sriracha, Worcestershire sauce, and Old Bay Seasoning in a medium bowl.

Add chopped fish to mayonnaise mixture and fold to combine. Cover and chill for at least two hours or up to three days.

Heat vinegar, sugar, salt and one cup water over low heat until sugar and salt dissolve. Place onion in a small nonreactive bowl; pour vinegar mixture over. Let sit at room temperature for one hour.

Lay flatbreads on a clean work surface or countertop. Spread about half of the smoked whitefish spread on each flatbread, leaving a half-inch border all around. Top with arugula and pickled onions.

Roll each flatbread, creating a long log about three inches wide. Wrap in plastic wrap and refrigerate until ready to serve.

When ready to serve, gently unwrap and, using a sharp knife, slice into one-and-a-half-inch-thick pieces. Place 2 pinwheels onto each plate. Use a toothpick to hold in place if needed, or for decoration.