Bring sauce to a simmer and carefully add the rum. If the sauce is very hot, the alcohol will flame on its own. If not, use a stick lighter to carefully ignite the sauce and continue cooking until flame dies out, 1 to 2 minutes. If the sauce is too thin, cook for an additional 1 to 2 minutes until it reaches a syrupy consistency. Add the orange zest and stir to combine. Immediately spoon the sauce over bananas and serve. Serve with waffles, crepes, or ice cream.