In a skillet over low heat melt the butter, add the onion, yellow pepper, fennel, and garlic.
Season with salt and pepper. Cook slowly for about 6 minutes until all are tender, transfer mixture to a bowl, add bread crumbs, and allow to cool.
Preheat oven to 375 degrees F.
When cooled add crab meat, mayonnaise, lemon zest, lemon juice, tarragon, parsley, scallions, and season with salt and pepper, to taste. Mix the ingredients well and stuff the shells. Bake for 25 minutes until warmed through.
Note: the crabs should be poached in a court boullion made with 2 quarts water, 1 chopped carrot, 1 chopped yellow onion, and 1 chopped celery stalk boiled with 1/2 teaspoon each black peppercorns and coriander seeds. Bring the mixture to a boil and after 10 minutes, add 1 lemon, thinly sliced. Let boil for 10 more minutes, salt the water, and poach the crabs.