Drain the crab and put in a bowl. Add the egg, green onions, mayonnaise, mustard, salt, pepper and breadcrumbs. Mix this altogether and see if you can shape it into patties. If it doesn't hold together, add more breadcrumbs. Use just barely enough. You don't want the mixture filled with bread.
If you can, refrigerate the mixture at least half an hour so the patties will hold their shape better.
Put the flour or breadcrumbs. in a pie tin or flat plate and season it with salt and pepper.
Preheat a large skillet and add the oil and butter, swirling to cover the bottom of the pan.
Shape the crab mixture into four patties, dredge in the flour or breadcrumbs, and place them in the pan.
Cook, turning once, about ten minutes, until golden brown.
Serve with lemon wedges and/or thousand island dressing.