Mix mayonnaise, Dijon mustard, Worcestershire sauce, lemon juice, and parsley in a bowl until smooth and pale yellow, about 2 minutes.

Fold in lump crab meat gently in a large bowl, preserving its sweet, flaky texture.

Season the filling with salt and freshly ground black pepper to taste.

For the topping, combine panko breadcrumbs, grated Parmesan, and melted butter in a small bowl until crumbs are evenly coated.

Scatter the buttery breadcrumb mixture evenly over crab filling in a greased 2-quart baking dish, then press gently with the back of a spoon.

Bake casserole in a preheated 375°F oven for 20–25 minutes until bubbly and the topping is deep golden brown.