  We study electronic transport across a helical edge state exposed to a
uniform magnetic ({$\vec B$}) field over a finite length. We show that this
system exhibits Fabry-P\'erot type resonances in electronic transport. The
intrinsic spin anisotropy of the helical edge states allows us to tune these
resonances by changing the direction of the {$\vec B$} field while keeping its
magnitude constant. This is in sharp contrast to the case of non-helical one
dimensional electron gases with a parabolic dispersion, where similar
resonances do appear in individual spin channels ($\uparrow$ and $\downarrow$)
separately which, however, cannot be tuned by merely changing the direction of
the {$\vec B$} field. These resonances provide a unique way to probe the
helical nature of the theory.
