1. Preheat the oven to 350°F. In a large mixing bowl, combine the crabmeat, mayonnaise, green onions, parsley, lemon juice and zest, salt, and cayenne. With a rubber spatula gently fold the mixture together.
2. Since you’re using jumbo lump crab, the last thing you want to do is rough it all up and tear the meat.
3. Once the ingredients are combined, drizzle in the melted butter and then immediately give it another fold to incorporate. Because the rest of the ingredients are cold, that butter will seize up quickly, so you want to fold it in as soon as you pour it, still being as gentle as you can. At this point, you have a really good crab salad that can be served cold on its own or used for crab cakes.
4. Add ¼ cup of the breadcrumbs and fold gently to mix. Divide the crab and breadcrumb mixture evenly among the 6 crab shells. Sprinkle the remaining ¼ cup breadcrumbs equally on top of each crab shell.
5. Place the crab shells on a baking sheet and bake until the internal temperature is 130°F, about 30 minutes. Using a good thermometer is crucial here because you really just want to warm it all up. If the mixture gets too hot, the mayonnaise will break, and you’ll just end up with greasy crab.