CRAB PATTIES: Place the crab meat in a medium mixing bowl, set aside.
In a small bowl beat egg slightly, whisk in mayonnaise, mustard, Old Bay, lemon juice, Worcestershire sauce, and salt. Pour sauce over crab meat, sprinkle with bread crumbs and parsley, mix thoroughly, but gently. Cover with plastic and refrigerate 1 to 2 hours.
MANGO SALSA: In a large bowl, stir together mango, avocado, corn, red onion, jalapeño, lime juice, parsley, salt and pepper, and a drizzle of olive oil, until well combined. Refrigerate until ready to serve.
Shape crab mixture into 4 or 5 equal patties. In a large non-stick skillet, heat butter with olive oil over medium heat. Cook crab patties until dark golden brown, about 4-5 minutes. Flip the patties, reduce heat to medium-low and cook until the other side is well browned, 4-5 minutes. (Depending on the size of your pan, you may need to cook in batches, do not over-crowd.)
To assemble burgers: Toast the buns. Pile salsa on the bottom buns, followed by a crab patty, a leaf of lettuce, and the top bun. Now devour!
Cook's Note: Serve leftover salsa with corn tortilla chips!