Made this last night. Arugula surprisingly keeps a lot of texture after wilting. Very tasty. Don't skip the pepper flakes, it isn't much and it adds dimension to the dish. I also agree with a reviewer from the original source that this would be great sprinkled with a bit of feta.
My fish is always in pieces and of varying thickness, so I use an instant read thermometer to check for doneness. Cooked long enough this recipe never fails to please!!