Preheat oven to 190°C (375°F). Lightly butter four ramekins or a small baking dish.
In a mixing bowl, whisk together mayonnaise, egg, Dijon, Worcestershire sauce, lemon juice, Old Bay, paprika, garlic, parsley, and a pinch of salt and pepper.
Add the diced bell pepper and celery if using, then gently fold in the crab meat using a spatula. Be careful not to break up the lumps.
Spoon the mixture evenly into ramekins. Sprinkle panko breadcrumbs on top and drizzle with melted butter.
Bake for 18-22 minutes, or until golden brown and bubbling.
Optional: Broil for 1 minute to deepen the color and crispness of the top.
Remove from the oven and let rest for 5 minutes. Garnish with parsley and lemon zest.