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-Perot 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.
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