tofubeast,
The information that you seek, can be found here:
http://disneyland.disney.go.com/disneyland/en_US/parks/dining/detail?name=BlueBayouDiningPage&bhcp=1
the Blue Bayou's hours of operation, coincide with the parks hours, so therefore will vary, depending upon the season.
Lunch only:
Le Special de Monte Cristo - Turkey, ham and Swiss cheese in a battered egg bread, lightly fried to a golden brown. Choice of two sides: Blue Bayou potatoes, seasonal vegetables or sautéed spinach. $18.99
I don't see any good reason, why a simple request such as yours, could not be accommodated. If I order that dish, it will be without the ham, I like ham, I just am not a big pork eater, thats all.
Last April, I made my reservation for two, three days in advance, no problem, however, seating was limited. So I figure, it all depends upon the season, to which you plan on visiting, however, just to play it safe, I would PS, as soon as I knew when I was going to be interested in dining there, even if it is a dessert only reservation.
They do accept walk up reservations, too, however the wait time, can be extremely long, and one might not be able to be accommodated for that day,
that is why I make ressies.