See if you can enroll in 5000 and 6000 level math/CS/stat courses
I suggest courses in probability theory, data science I and II, information theory, complex systems. You could also do an independent study in control theory. You can also build off your MechE background in a computational direction by taking computational solid mechanics, numerical methods for engineer [sic], and multiscale modeling
IMO, combining generalist skills like CS and DS with domain expertise is the best way to have a successful career.