  We demonstrate that the longitudinal single target-spin asymmetry in
exclusive $\pi^0$ production in $ep$ collisions can give access to the
imaginary part of the gluon generalized transverse momentum distribution (GTMD)
$F_{1,4}$. Such a longitudinal spin asymmetry that results from the
Coulomb-nuclear interference effect, leads to a characteristic azimuthal
angular correlation of $\sin 2\phi$, where $\phi$ is the azimuthal angle
between the scattered lepton transverse momentum and the recoiled proton's
transverse momentum. We also present a numerical estimate of the asymmetry for
the kinematics accessible at EIC and EicC.
