Ordered sandwich and realized it had lettuce that had a brown spot that was slightly slimy. removed it. ate sandwich. could this harm breastfed baby?

Food, lettuce: lettuce turns brown and mushy when it ages and is a natural process that should not harm you or your breast fed baby.

Very, very unlikely: The dangerous salmonella does not produce a visible sign. This was probably just a bit old or stored w/ moisture. Removal was good and if you are not ill - there's close to no risk of your milk being bad. Don't worry - that can be more harmful to both of you. Unless you know the restaurant well, eat home cooking to avoid risk , save $ and know the nutritional input if you really care about it.