Your bladder is going to be a little bit "irritated" after the BCG treatments, so I would hold off hot chili peppers for a couple of days.
As I have said before (and the old timers here are probably tired of hearing it) the time when we should have been cognizant of what we were eating (if indeed it has an effect) would have been about 20-30 years ago, when whatever damage to our DNA was being done. That said, it never hurts to eat, in general, a healthy diet with the requisite fiber, vitamins, and minerals.
Sara Anne